I know I babbled about Cool Iris before. It's a Firefox Add-On that allows you to hover your cursor over a link and have a kind-of window shade unfold to show you what's at the link without actually leaving the page you're on.
I downloaded PicLens a little while back and while I thought it might be kinda cool, it was still a little buggey. It seems they've worked out the bugs, and yay, I pronounce it awesome. The link will take you to the version for Firefox on mac, but there are links for other browsers and for Windows as well. There's also, apparently something for you WordPress bloggers that I didn't look at too closely, because, I'm not one of you, but I bet that's cool too.
Take the tour and download this immediately.
Update: One thing that still doesn't work when you're using PicLens...If you're searching GoogleImages for some generic picture to use on your blog...it's not very useful. If you're doing the normal search and just going through the pages of pictures, you can just drag the picture to your desktop (at least on a Mac) and bingo. If you're looking through them in PicLens, you can't drag it to your desktop and you have no idea what page it's on in the GoogleSearch. Technically, this probably doesn't count as a bug, just a missing feature that would be nice to have.