If there's an Apple store nearby, I bet you could go there and use one of their ipads to look up whats available. Not ideal, but one thought.
Also, iBook isn't the only option: Amazon has the Kindle app, B&N has a Nook reader app, Google has an ebook app and ebook store, etc. iBooks will read ePub format books just fine regardless of where you get them; I have several titles from fictionwise.com that I read within iBooks.
Plus there's Stanza as a general purpose ebook reader and Overdrive too -- Overdrive being useful if your public library has a system for loaning ebooks. (mine say's coming this month, so I don't know if there is or will be much).
With this said, there are a number of doomsayers claiming Amazon will remove the Kindle app from the App store rather than kow-tow to Apple's Subscription Model requirements. I'm thinking I'd worry about that if/when it happens more so than making a choice based on something that might happen. Plus, no telling how it would truly fall out, I'd be surprised if Amazon abandoned the iOS platform. (not impossible, but I'd be surprised)