This year, i've mostly been using:
- whichever exchange client comes with the phone - and they're all clunky (moto's is ok, se/// is pish, htc is ok, dataviz roadsync is ok too)
- google maps - a lot. buzz enabled? meh...
- facebook - while clunky sometimes (and tends to freeze on some posting), it's become my primary facebook interface
- evernote - except it's not in marketplace on current phone... grrr. it's good.
- etherial dialpad - fun, kids like it...
- tricorder - fun fun fun... (and useful for wifi finding...)
- beebPlayer - when i'm desperate for TV
- compass - never sure why I bother though...
- [google] finance - if I can't bother finding out how bad my portfolio is elsewhere
- goggles - cos it's fun sometimes (works well too..)
- [google] sky map - for entertaining the kids on occasion
- linkedin - it's pish
- last.fm - very nice indeed, but don't use it much
- layar - dunno why I bother...
- newsrob - but always forget to sync it up (very good though)
- pkt auctions - for when I have ebay on the go
- tv guide - nice, but seems slow
UPDATE: Sept 2010 right about here.