I use Picnik. It's pretty basic, but does everything I need. I have Photoshop, but I never use it. FYI: Picnik can be a little slow to load.
I really didn't like the Windows photo editing site (Windows Live, or something like that). Nor did I like Pixer--annoying.

I use Picasa for basic editing and uploading to google. It's easy and fast. Not nearly as powerful (or anything like) Photoshop. But it gets the basics done easily (crop, color, brightness/contrast, red eye, etc)

I use fotoflexer. No need to sign up/log in, and the ad support is fairly un-obnoxious. It has some fun effects and tools, and allow you to download/upload from multiple sites as well as your computer.