Most office parties feature a bar, maybe some light jazz, some nuts to snack on and a few streamers for background ambience.

But lately a growing number of Silicon Valley companies are holding their parties backed by a 40-foot Tyrannosaurus rex skeleton, a coral reef teeming with 4,000 Philippine day-glo fish and a domed planetarium showing how super novae explode.

Last year, the new $488 million California Academy of Sciences building made a big splash as a public museum when it opened in San Francisco's Golden Gate Park. But in a trend that has surprised even its own planners, it also has emerged as one of the hottest night spots in the Bay Area.

Despite a rental fee that can total $30,000 a night, the museum has played host to scores of corporate events, tilted heavily toward tech, from the launch of video game phenomenon Spore to a 15th anniversary bash for WIRED magazine. In the past year and a half Google, Microsoft, IBM, Salesforce.com, Adobe, Intel and Oracle all have rented out some or all of the museum for parties and other events.

"We're a company of nerds, in the best sense. We really like to learn about science," said John Lilly, CEO of Mozilla Corporation of Mountain View, which hosted a company party for 250 people last Wednesday night at the Cal Academy.

Lilly, 38, whose company makes the popular Firefox web browser, sipped a cocktail a few feet from the museum's swamp exhibit