Flip Frames allows you to upload images into a variety of “frames” and then super-easily add captions, speech bubbles, etc. You can then email the link for posting, or embed it with the code they provide. It actually looks a lot cooler than I’ve described.
It also lets others leave comments on images you upload and, more importantly, it gives you a private option so that not everyone has access to your creations.
Unfortunately, you can only upload images from your computer now and not grab images off the web. It would be nice if that feature could be added in the future. You also have to register, but the process is quick and easy.