Any tips for phone stability? My Moto Droid has seen great performance improvements with each new Android version, and has been much more stable and reliable with each version release.

Recently I was in a situation where the phone just didn't think it had a cell signal, and then wouldn't disconnect the call that it couldn't place because of the non-existent cell signal.  Ultimately I had to reboot the phone to get it to be usable again.  This happened when I really needed to make a call and was a huge hassle.  Having a smart phone with tons of data network features is great, but I still pay more for minutes than I do for data (thank you US carriers...) so not having it function as a phone when I need it is very frustrating.

I'm running Android 2.2 and don't use many widgets nor do I keep many programs running that use background services (don't usually keep GTalk connected, etc)

Does anyone have any general tips or apps to avoid to help keep my phone stable and reliable?
Well, it sounds like you don't want to monkey much. (Otherwise I'd recommend rooting and then installing vanilla 2.2, which is going to be the most stable of any release). It sounds like the problem you experienced is just a flat out bug and might not have anything to do with any apps you are running. 

On the other hand, are you using any task-killing apps, or battery saving apps or anything that might be screwing around with system processes? If you are, I would recommend getting rid of them -- they are generally cause more problems in the long-run than they solve. If not, then I'm not sure what to tell you other than file a bug report or call Verizon and complain, but neither of these options will fix your problem. 

If the problem was at root a signal issue, there is a way to update cell tower information, which Verizon can help you with. It involves dialing a number and allowing an automatic update.

BUT, if you did want to monkey a bit, then I do suggest flashing the vanilla froyo. It is just a little intensive, but wouldn't take you longer than an hour. If you want information in this regard, I can provide you with a website that includes step by step instructions.