Google Chrome just got an extension called Hover Zoom that allows you to see a full size image from a thumbnail without having to click through. It requires a direct link from the thumbnail to the source image to work, so some sites' code won't be compatible. I've been test running this for a little bit and so far I like it.
I've set a key to turn the feature on, so when I hold down the SHIFT key and hover over a picture it pops up the full size image. That way if I don't want to see a preview it's not constantly putting things in my way. This is a great tool for searching images on sites like Amazon.com or Flickr.com. However it's speed depends on the speed of the server, so it can be slow at times.
I'm happy to have this tool in my toolbox, but a lot of the image searching I do is through Stock Exchange and Google Images which already provide a feature like this.