I have a big bag of ~50 jalapenos in my freezer, frozen less than a day after being picked. How long will they last in there, and how will I know they've gone bad?
First off, pretty much everything stored in a properly cold freezer (0°F/-18°C) will be safe to eat forever.
The flavor will eventually go, e.g., by getting freezer burn and also by enzymatic degradation (if not blanched). How long this will take depends on exactly how you've stored them. In general, airtight packaging with no air inside seems to be best. For example, vacuum-sealed thick bags work well. Cheap, thin plastic "storage" bags don't work well. You can get around 8 months according to UNL. Colorodo State believes you can get 12 to 18 months.
edit: It also occurs to me that it matters what freezer you're using. The one on my fridge, for example, has fairly large temperature swings (yet mostly stays below 0°F) and automatic defrost, it freezer burns things much quicker than my chest freezer (which has a temperature variance of maybe 2°F, staying in the -3° to -1°F range)
I have a bag of frozen Jalapenos from 2008 that still have a good flavor and spiciness. They'll last about as long as you can stand to not eat them, as far as I can tell.