First and foremost, I think you need a "News" section, which does exactly what it says on the tin. Information about significant occurrences within the band that may interest fans/people who want to hire you. What you all had for lunch is irrelevant, writing half a song is irrelevant, getting ready to record a new album, however, is pretty important to let fans know, likewise, lineup changes or whatever can go in here.
A "Band History/Members" section is important I think, but keep it concise. I like to read a brief band history and then have a list of current members, what they play and perhaps a photo of each member alongside. A seperate section noting previous members and what they played is also important.
One of the key things you're missing from a commercial perspective is a "Shop" section, to sell any of your merchandise. They can't buy it if you aren't selling it.
If you're reasonably well established, with a few CDs under your belt, a "Releases" section is nice, so people can look through your band's current CD and previous releases. It works pretty well if you include a few samples in this section.
The layout is just as important as the content. Everything should be clear, not too cluttered and all features should be easy enough for anyone to use.