My single favorite non game app is notebooks by alfons schmid. Its my favorite text editor app that allows me to work on my writing (novel chapters, tv scripts) directly on my phone.
Next up is PhotoForge a kind of mini photoshop that gives you access to a wide range of features to edit your photos, it works brilliantly at lightening up very dark photos, in effect saving them from deletion. Well recommended.
Air Sharing Pro, this turns my 3GS into a portable storage drive so i can put a wide range of files onto the phone without itunes from my mac. I mainly use it for PDF viewing, when my finished writing is saved in that format. This does iDisk too so i don't need a separate app.
Two new entires are Autostitch and Anigif. Autostitch like the name suggests stitches photos together if i want to create a more panoramic picture. Anigif lets you create movies out of photos that look like stop motion animation and is very cool!
Thats it really, for some reason i cannot stand just dumping every app i have on to the phone and so i choose very carefully the ones i will use on a regular basis, where some people have 128 apps (8 pages) i have only 14 extra apps.