Chrome: Save yourself from clicking through thumbnails links just to peek at the bigger picture. Hover Zoom automatically enlarges thumbnails to their full size without clicking through.
By default Hover Zoom works automatically and on all thumbnails with links it can properly parse — direct image links, as well as on popular sites like Amazon, Flickr, Deviant Art, Facebook and more. If you'd like finer control over when and how thumbnails pop up, you can blacklist sites, tweak the popup and fade time and assign hot keys. You can use hotkeys to toggle Hover Zoom (it will only work when hot key is pressed) and for full zooming (image will enlarge to full size of the browser window).
Hover Zoom is free and works wherever Google Chrome does. Have a favourite tool for image wrangling in Google Chrome? Let's hear about it in the comments.