The only ones I've actually seen lately are Letz Zep, who played the Epstein last October - they are pretty good and the singer is from Liverpool. Worth looking out if you're a Zeppelin fan.
I've seen a few online, who are worth listening to. The female Iron Maiden tribute, The Iron Maidens and Zepparella, a female Zep tribute are interesting. There are the Glimmer Twins (Rolling Stones), Vesbim Floyd (Pink Floyd), and Rain (The Beatles). There's a Dutch band called The Watch who regularly do Genesis tribute shows, but also produce some decent original stuff too. There's a guy called Elvis Prestello, who does Elvis Costello covers, but in the style of Elvis Presley - make of that what you will!