Dropbox is a useful way to back up a lot of different things on the phone - the mention of 1Password (which we use) reminded me of it. You can also use it to share files among computers - e.g. I can edit a spreadsheet on my Android, my iPod Touch, my work laptop, my home desktop…
If you want to get Dropbox, which is online cloud storage and is free for the first couple gig, PM me and I’ll send you a link that gets us both a bit more free storage :).
If you do purchase stuff, I assume it would be on your own iTunes account vs. a work-based account. If so, synch it to your own computer at least once and everything you buy will be stored there as well, so if you do have to give up the iPhone, you will have access to it in the future if you get your own iPhone or iPod Touch. You can re-download apps even if you haven’t synched, and now you can redownload music as well, but that was not always the case.
Utilities that are nice to have: We use PlainText as a text editor - it links directly to your Dropbox account, vs. the built-in notes application. Simplifies note-taking.
CamScanner: lets you snap a picture of a document and turn it into a PDF. I’ve taken such documents and OCR’ed them on my desktop; there may even be an OCR tool available for the phone. There’s a free version of it with some page limitations; I plunked down a couple bucks for the pro version of it on my Android. Typo Knig has an iPhone and hasn’t used it much… yet.
1Password is a godsend. Using the Dropbox sync, you actually have to sync it once from a desktop computer. You can get the trial version of the desktop software, do the setup / sync, then after that you don’t have to have the desktop version installed. Of course you might find it useful enough on the desktop that you want to pony up the 30ish dollars (the handheld version is 10ish, I think).
Games: Cut The Rope is cute, addictive, and a lot of fun. Like many games, there’s a limited version for free, 15ish levels, and you can pay the 99 cents to get the full version.