Does WiFinder actually do anything that the built in Android wifi detector doesn't?
Personally I'm fond of Ringdroid which allows you to take any MP3s and cut out a selection for a ringtone or an alert. I also really like Recordoid, a dictophone app which includes a widget which is handy to quickly start a recording. Phoning pidgeon allows you to set a specific number which, should you get two calls from in quick succession, will activate your ringer even in silent mode in case you've misplaced your phone. I have a spare paygo phone for emergencies and I set that number, though thankfully I have yet to have to use it for anything but tests. I believe the same group also made Carr Matey which allows you to mark on a Google map where you parked your car, using GPS, and can thus direct you back to it.
Tricorder is a lot of fun, though not hugely useful for any practical purposes, and this may sound silly but I've gotten a remarkable amount of use out of the extremely handy flashlight app. It's amazing how effective it can be, and more so than just loading the dashboard.