I am considering purchasing an iPad and one of the uses would be to read books. But I can't find a way to browse the iBook store and see what books they have available without actually owning an iPad. Is it accessible via iTunes?
Although there is no way to browse the store directly, there is this website which searches the iBookstore for a particular title or author. It also searches the Kindle and Nook stores.
Even since iTunes 10.3 this browsing is possible from a Mac or a Windows OS. Browsing(filtering by rating and so on) iTunes is not as pleasant an experience as on the iPad, so you might also choose to browse the store from an iPod touch or an iPhone if you lack an iPad for browsing the store "natively".
Pre iTunes 10.3, the iBookstore was only available from the iBooks app on an iPad, iPhone, or iPod touch. If you know someone who has any of those, you could ask to look, but you cannot see in iTunes.