Radio for your iPhone! This app lists thousands of radio stations broadcasting on the web, broken down by genre. You can bookmark your favourites, search, browse the top 500 – as decided by whom, it doesn't say – or add your own streams.
The interface is clean and simple, and because many of the streams will play even over EDGE, you're never short of something to listen to. (O2's terms and conditions prohibit continuous streaming of audio content, but we're hoping this doesn't count.) It supports AAC, MP3, PLS and M3U streams – no BBC, but you won't care.