Flickr has recently teamed up with Picnik to provide photo editing tools right in the Flickr window. Now each photo has a handy little "Edit Photo" button that will take you over to the Picnik interface. I played around with it a bit and must say, it's a nice tool to be able to access especially if I'm not at my home computer.
Here's a before and after of a shot I took at Buntzen Lake.
I didn't change a whole lot, just softened the photo and added the vignette effect, but I think it makes all the difference.
There is also the option of adding text and shapes so I was able to create a nice Christmas photo.
I definitely think I will be using this tool more in the future!