According to 1up’s David Ellis, the PS3 Slim is coming this August, and there will be some sort of tie in with Madden NFL 10 which releases August 14th.
Ellis says in the latest Listen UP Podcast:
“It’s gonna be in August. Everything I’ve heard says it’s coming in August, it’s tied with Madden.”
If we are looking at a August release date as 1up is stating, then expect the PS3 slim to be announced at this year’s GDC Europe/Gamecom in Cologne, Germany. Sony is holding a 3 hour press conference there, on August 18th which would be a prime venue for that time of an announcement.