I don't have enough post to link so just Google what I posted if you want them they'll all be on the top results.
Open with Photoshop. A Firefox add-on that adds a option to your right click menu to send the image directly to Photoshop. It also adds a button icon.
Script bay. A launch platform for all your scripts as a extension.
GuideGuide. Another extension for making guides.
CSS3Ps. Easy image conversion for CSS3
Filter Hub. A extension platform for filters with a lot of good enhancements like painting on your effects,favorites, and many more.
TypeDNA Font manager. A extension that lets you sort out your fonts,build custom libraries,access font stores, and a bunch of other cool stuff right from Photoshop.
Preset Viewer Breeze. A standalone tool for viewing your styles,brushes,actions,psd, and more. The options to extract images out of them as well. You can directly send the selected item straight to Photoshop. IE Load a style set into it and find one you like and send it directly to PS without having to move it to your styles folder location.
Site Grinder. PSD to html conversion.
This last one is not really related to Photoshop however it lets you bypass a annoying as hell flaw in the 64 vs 32 game.
Sandboxie. It's for running programs in a virtual sand-boxed environment. If you have 64 and 32 PS you most likely know you cannot multiclient which sucks. With sandboxie you can get around this limitation. It's better than having to close it down just to use a 32 bit only filter. You can also achieve this with a virtual machine but that is overkill lol.