In no particular order:
1. Possibly 3D turn by Turn Navigation, that could bluetooth to an external GPS. (although in reality I have several GPS units now, so maybe I wouldn't pay for it, although a lot of people no doubt would). I'd bet you could at least $49 for something like that.
2. A great task manager such as OmniFocus based on the GTD system. An OmniFocus iPhone app would definitely get $29 out of me.
3. An app to use the camera to image a business card into contacts. That OCR function exists on some HTC phones. Perhaps $ 19.95 would work there.
3. A decent non-browser based front end for orb.com, with the ability to schedule TV recordings, access photos etc. $ 29
4. An app to access AppleTV, the Xbox 360, or the PS3 over the net. Get content from the devices and upload photos . $ 19.95
5. Some sort of aggregator for social networking sites. $ 19.95
6. A really nice Twitter client: $ 12.95
7. App that will allow you to Geotag photographs using either the phone's location ability or again bluetooth to an external GPS. $14.95. (Then of course the ability to pin those photos to Google maps)
8. A very good Bible program ( 2-3 translations)
9. A really good e-book reader, $ 19.95
10. A good internet radio front-end. $ 14.95