Our Toaster isn't doing well, planning to replace it with a toaster oven to get some more versatility on the counter top. What features are good? I've looked and there are ones ranging from simple $25 models to $250 with a laundry list of features. Just wonder what's useful and what's not, hope to find a good one that's $120 or less really, but I'm willing to pay extra if it's worth the money.
I actually debated asking a similar question last month, as I managed to set mine on fire the day after Christmas, and based on the new one I got, differences I've noticed (mostly features I miss from the old one; also a few things I've noticed at my neighbors and mom's house.
Insulated top; If you frequently run out of space in your kitchen, and need to keep stuff on top of the toaster oven, it comes in handy. (and some allow the top to open up so you can expose the top so it could be a bread or plate warmer)
Is the rack connected to the door so, when you open the door, the rack pushes out a couple of inches, so you don't have to reach in to extract things and risk burning yourself? (okay, I admit, there's a few drawbacks to this; it means the rack isn't easily removable to be cleaned or if you need to pull it all the way out because there's something that got pushed to the back, and the next item)
Multiple racks or rack heights. The different positions might be useful for the broiler, but the multiple racks really aren't that useful; things won't toast right when they're blocked by another level, and they don't tend to cook evenly when in oven mode, either. (maybe if it's a convection .... it's my neighbor's toaster oven, so I haven't played enough with it) If you leave both racks in there, then you've barely got any space in between to grab things out, so you're risking burning yourself. (and well, they don't have that last feature where the rack pops out when you open the door)
Location of the controls; some are on the side, some are on the bottom. Controls on the bottom are more prone to getting damaged by things getting pushed around on the counter, but I prefer it for a few reasons -- (1) the toaster oven's narrower, as there's no wasted space to the side; (2) the door opens higher up; this means you can have a large plate on the counter without it getting in the way when you want to open the toaster.
Convection ; some have it, some don't.
Broiler ; not all can do broil (top element) only.
Depth of the unit; some of them bump out so they can fit a round pizza; if they also have a little bracket so you don't accidentally push it up against the wall, there's hardly any space left on the counter.
How exposed the elements are; some of the newer ones have grills over the elements, I haven't had mine long enough to see if that'll protect it from melted cheese dripping on 'em, which I think was the cause of my toaster fire.
Turn-dial vs. brown-ness setting. I don't know how to explain this one. All of the toaster ovens in the stores I looked in have a dial, where you have to turn the dial past 10 min, then back to the little reference marks for the darkness that you like your toast; My old one just had a setting at the bottom, you set it to toast, and hit the button. If you wanted to shut it off, you opened the door. Of course, with this style, there wasn't a timer on the oven, either.
Turn-off-via opening the door : Some do, some stay on. I'm used to it, but of course, if that's the only way to shut it off, that also means you have to open the door to shut it off when there's a fire inside, which means better airflow. (or unplug it, but when the plug's on the other side of the toaster, that one's not a great option, either).
Electronic controls : I personally view it as something else to break, but they might be able to do something special; I've never bought one, myself.
Cord length ; only really a problem when you've got an old kitchen that doesn't have a plug every 12" or whatever the new standards seem to be; but you really don't want to plug a toaster into a power strip if you can help it, so if you know you're going to need to run it 3' down the counter, check the cord length. (and which side it attaches, just in case you're then going in the wrong direction with it)
Crumb tray. I hear other people use 'em. They're supposedly important so you don't catch the thing on fire.
Accessories. Some come with a little tray to use; some of them also have a little insert to turn it into a broiler pan (so you lift it out of the pan a little bit, so it won't stew in whatever drips off). And I understand that you need some air flow around the pan, but in my opinion, something's wrong when the tray that comes with the toaster is 1/2 the area of the rack; it's like they weren't even trying, they just tossed in a tray from some other oven. Others come with a little tool so you can pull the rack out so you don't burn yourself (which then gets lost or broken and thus sucks)
Size. If you tend to make toast for lots of people at a time, then some of the larger toasters might be worth it; If you're single, the 6 or 8 slices of bread at the same time (but not the size of bread you like; you can only fit two of those) toasters might be a bit overkill) And they now seem to measure themselves by 'size of a pizza I can fit', which makes no sense to me, as everyone knows the correct way to size toaster ovens by pizzas is how many halves of an english muffin you can fit in at one time (to make english muffin pizzas ... avoid the bagels, as sauce and cheese drip out the middle)
... so um ... those are just some of the features I've noticed. Some people might care about the 12" pizza thing, I personally don't. The timer vs. push button for the controls are likely a personal preference, as is the attached rack to the door vs. height adjustable/removable rack.) The only really must-have is the removable crumb tray which Allison mentioned. (even though you can go years without worry until there's a fire)
If you don't care what your appliances look like, the primary feature to look for is the ability to get in there and clean the thing. Toaster ovens are flexible and convenient, but at the end of the day the worst feature to not have is a way to clean them.
Depending on what else you have available to you, I found that a counter top oven works very well for me. I have the ability to toast, but it also is an oven, a broiler and a convection oven. There have been several times when I needed to have several things cooking at the same time (American Thanksgiving) and I was able to do the yams in the countertop oven, or a pie, or even a roast chicken once when the trickier item was taking up the main oven. If you already have double ovens, that probably won't matter as much to you, but I have a small house and a single oven and the counter top model is a blessing when we're entertaining, or even when I want to heat the kitchen a bit less than the full oven.
For me, then, being large enough to take a casserole or a pie was important, and the convection feature I use all the time because smaller ovens tend to be less even for their heat.
Many of the other issues have been covered above, but allow me to suggest one more: Toast timing mechanism.
On some toaster ovens, there are separate timer controls for toasting and for the oven. The coaster control will be in terms of toast darkness (or maybe 1-10), while the oven timer will be in terms of minutes. This is in my opinion the superior way to do it.
On my crappy Euro-Pro toaster oven, there is one timer for both the oven and the toaster. I have no idea how long it takes to get toast to my desired doneness, and the timer doesn't quite have the precision to handle times like 2 minutes, whereas for an oven that sort or precision never seems necessary.
One thing to consider is whether you want it for a toaster mostly or an oven mostly.
If you mostly want toast, think about how much air you're going to have to heat to get the bread toasted--a tall oven will work more slowly and be less efficient than one that's pretty close to the bread on both sides. This is also helpful if you think you'll be broiling in it.
Conversely, if you think you'll be putting larger things in it, you'll probably want more room.
My old work had a tall one (probably 8 inches inside clearance), and it took approximately one million years to make a piece of toast. I started toasting a bagel the day I left and four years later people are probably still waiting for it to brown.