I haven't really gotten myself into online photo editing and effects software because they usually fall behind Adobe Photoshop, but I tried one which is worthy of not just trying out, but of actual use. The effects are fun, and can be used to create wallpaper, images for your girlfriend/spouse, but can be of real use when designing a logo, either to use as is, or to get some ideas.
Head on over to BeFunky to try out the great effects they have! From Cartoonizing to the Warholizer you have 9 effects, and some sub-effects in each.
Update: Note that BeFunky launched a Plus version of the online photo editing and creation application. The effects described in the article are not free anymore, but only available if you have upgraded to BeFunky Plus. Modern photo editors like Paint.Net support basic effects as well.
They can all be fine tuned in a lot of ways to give you the perfect result. getting photos is alse really easy, you can upload from your hard drive, get from a URL, get one from your webcam, or even from a photo sharing site.
There is also some gentle comedy throughout the site, from the design itself to some effect descriptions "Patriotic: Ask not what your photo can do for you, but what you can do for your photo". The lightheartedness, the features and the quality of the effects themselves makes this site a worthwhile visit which takes its rightful place in my bookmark list. Take a look at me at the Atomium in Belgium below, awesome effect!
Update: Please note that you need Adobe Flash to run the site. The site has been improved in recent time, which you will notice not only when you look at the number of effects, there are more than three times as much now available, but also the other image editing options available on the site.
The effects are really nice and some may even remind you of what apps like Instagram offer. Whats more, you can upload photos not only from your computer but also from sites like Facebook, Photobucket, Flickr or Picase. And if you have a web cam connected to your PC, you can even use it to add effects to your profile shot.