I'm wondering what beef roasting joints will come out of the slow cooker best? I'd like to be able to slice it rather than pull it though. I've tried before with Brisket, it was delicious, but fell apart on carving. I'd like a cut that is soft but still sliceable.
You are looking for a lean cut.
The reason meat "falls apart" after a long, slow cooking process is that the connective tissues and fat dissolve/gelatinize.
You still risk this in any cut if the moisture level gets too high, but I've had great success with pork tenderloin in a slow cooker being still sliceable after 6-8 hours. I don't see any reason why beef tenderloin would be any different.
Another option is heart... It's a different type of muscle and it doesn't fall apart after cooking, but it's got a narrow window between great and shoe leather.