Neopwn2 (on its way)
Formula1 (currently using the timings app but nowhere near as good as the full one)
Stealth Tones (currently using some mp3's
LinkedIn (have to use full browser)
Nasa App (have to use full browser)
Blackberry style Exchange integration
TomTom (currenly have Sygic but prefer TomTom)
nice Facebook App (one being worked on)
---an app that can globally format the screen whenever the phone is held vertically(yes, rotation), whether in the phone, file manager, internet browser, etc..
---3D RPG..
---oh yeah, a fully working GBA emulator / PS1 emulator...
My dream application would be a completely working and fully featured calendar application, like SBSH Calendar for Win Mobile or Symbian S60. It should also come with a fully customizable desktop widget of course.
GPE Calendar is a good step forward from the default calendar, but the widget for example is somewhat lacking.