Photobucket is a huge social image site that lets you upload, manage and edit your pictures as well as share and host them on other sites like Facebook, MySpace and Twitter.
Photobucket has two main focuses. Searching and browsing in Photobucket's huge categorized library is easy, and a pretty impressive resource of images. Photobucket's categories are more fun than other sites, and in general it attracts less serious photography than sites like Flickr. Here you'll quickly be able to find funny images, cute messages and icons, amongst other things.
Registering for a free account gives you 500 Mb of space to store images; less than Picasa's gigabyte, but still enough room for lots of images. You can perfom simple edits, like red-eye removal, cropping, rotating and resizing, and organize your pictures in folders. There are lots of regular Photobucket competitions that you can enter or vote in.
Photobucket has cleaned up its design a lot, as it used to be quite messy. Compared to Picasa and Flickr, it's still pretty heavy on ads that aren't always very pretty.
If you're looking for a reliable and easy way to upload, store and host your photos, Photobucket is a great web app for just that.