Tomorrow, YouTube will be showcasing its first live stream as it broadcasts its YouTube Live celebration, which will bring together a host of celebrities, musicians, and notable YouTubers for a massive event in San Francisco. The show will be streamed on YouTube beginning at 5 PM PST, and will include performances from Katy Perry, will.i.am, Joe Satriani, Tay Zonday (the Chocolate Rain guy), and a number of other musicians. I’m personally looking forward to a special appearance from the Mythbusters team.

YouTube hasn’t yet made any announcements regarding a livestreaming service for regular users (which would pit it directly against services like Ustream) but it won’t be surprising if we hear from them tomorrow about the company’s upcoming plans. We first heard about possible streaming functionality back in January, and later confirmed that it would be coming some time this year.

YouTube’s Chris Di Cesare says that the event may be the first of a series of annual live-streamed get-togethers celebrating the year in viral videos. We’ll have another post tomorrow with some of the highlights.

Update: There have also been rumors that the event will actually be powered by Ustream or another third party.