Being on the road this summer with ZZ Top puts Aerosmith in a unique position for the Boston rockers. As guitarist Joe Perry rightly told us of the little ol' band from Texas, "They've been together longer than us." Not many acts can claim to have outlived Aerosmith, and even fewer can last so long with the original lineup. Therefore, it's that much more amazing that 2009 marks the 40th anniversary for bandmates Billy Gibbons, Frank Beard, and Dusty Hill.

Let that digest for a second -- 40 freaking years! Obama is the eighth president ZZ Top has recorded under, the Beatles hadn't broken up yet when they formed, most of today's pop stars hadn't been born yet, there was no hip-hop, it's their fifth decade of touring, and on and on. As most bands are celebrated for a decade together, we decided to ask Gibbons the secret of a happy band marriage. "I think first and foremost is the fact we still enjoy getting to do this more than anything we could imagine and somehow that translates into the nightly performance," Gibbons says. "Those two hours on stage, that's the real payoff. That's when we get together and we may not know what each other is gonna do. Some of it is because we're trying to outguess the next guy, trying to think of what he's gonna do next."

That the three musicians can keep surprising each other after probably doing more than 5,000 shows together (200 a year for 40 years would be over 8,000, so 5,000 is actually a conservative estimate), is remarkable, but Gibbons says they love to stump each other on stage. "There are a couple of spots where we'll poke fun at the other guys, saying, 'Hey, let's go back to 1973,' and you've really got to be on your toes to get it all right," he says.

To commemorate the anniversary we asked Gibbons for his essential ZZ Top albums, the first of which was a surprise. "'Rhythmeen,' released in '96 says it quite effectively. If you like ZZ Top's earlier material like say, 'Rio Grande Mud' and 'Tres Hombres,' it's all about 'Rhythmeen,'" he says. "It's got more of a bluesy feel like our earlier material and at the same time, our hardcore fans likened it being not far from Black Sabbath-style heavy metal."

As for the rest of his picks? "You could ask anyone with the history of the band in mind and 'Tres Hombres' always comes up a winner. Lest we not forget, 'Mescalero,' which is way out there," he says. We'll go ahead and say you can't go wrong with any of these selections.