oneforty is your Twitter outfitter, with tons of resources for all things Twitter. Currently, it is tracking 1800+ apps that make Twitter even better.
WOW! I have probably tried 5% percent of these 3rd party Twitter apps! When am I going to find the time to swoosh around for more juicy ones? At least the 'Essentials' and 'Most Popular' sections on the site should be good indicators where to start. It is just amazing, how much Twitter has evolved the last couple of years. Oops, I mean Twitter 3rd party applications! When will Twitter itself decide to move forward a bit? :)