wheresthegig.com is a distinct improvement on google calendar. It shows gigs, unconfirmed gigs, cancelled gigs and rehearsals as different colours, handles blackouts (non-availability), sends out updates and reminders to the band automatically. It also allows you to export the gig list to a google calendar if you have people who won't use wheresthegig (there's usually one in each band).
If you're in two bands, it also gives you a 'composite' view of all your gigs.
Seeing uk_lefty's comment, when you enter a gig it will also tell you whether people are unavailable at the time, so you know whether people booked off before or after the gig was confirmed. It will also allow you to list deps and offer the gig to someone else if someone is blacked out for a gig