The first one is the rumor that the 17 inch iMac is not long for this world. Lots of places have covered this, including our own Forever Geek, logistically this makes sense, so I won’t be surprised if it ends up happening.
The other big one right now is that we might see new iMacs and Macbook Pros at WWDC. Apple Insider has the scoop from the ever trustworthy “Wall street Analysts” who are guessing that Apple will unveil new Macs at WWDC along with the full feature revelation of Leopard.
I don’t think either of these rumors requires much more than little educated guessing to manufacture, and I believe there is a high probability of both of these being true….but I think they’re just educated guess at this point, and not inside info.