Apple's yearly developer conference should see iOS 8, OS X 10.10, and likely some hardware.
Intel Xserve July, Mac Pro (Intel PowerMac) in August?
Meanwhile, PowerMac revisions (Mac Pros) are expected to make the transition to the recently announced Core 2 Duo processors (codenamed Conroe). These processors are expected in July.
ThinkSecret speculates that the PowerMac revisions would come at WWDC, and indeed, MacRumors has received confirmation Intel PowerMac revisions ("Mac Pros") are to be announced at the WWDC Keynote which takes place Aug 7-11, 2006.