I've heard that Musical Box and Garden Wall are the most popular of Genesis tributes, but there's so many out there!
Also, Adelaide's The Zep Boys are a good LZ tribute.
I saw Musical Box perform about 15 years ago, and they were incredible. They sounded like Gabriel-era Genesis, they looked like them, they even had the same type instruments and amps that Genesis used to use. The singer did all the crazy elaborate costume changes that Gabriel was famous for. I don't think that Musical Box could have been any better.
There is another LZ tribute band that is a lot of fun - an all girl band named *** Zeppelin. They don't sound that much like LZ, but they sound good and their shows are fun.
The Australian Pink Floyd are amazing. I've seen them on tv and was quite impressed with them. Great attention to detail in their performances/arrangements.
Saw an interesting item on ebay yesterday - "Their Hispanic Majesties Request"...a cd anthology of Hispanic bands doing Stones covers. I might have to order that one!