Here's a fun one: I Write Like... It's pretty simple: you copy/paste a chunk of your writing into the window, and the big voodoo science algorithm will compare you to 50 different writers and tell you which one you write the most like.
You also get a badge and the code to display on your website/Facebook. It's just a bit of fun. (I also got Isaac Asimov and Agatha Christie.)
(The people who put this up also make a diary app, Mémoires. I haven't used it — I'm too lazy to keep a diary — but it looks perfectly cromulent.)
I use Pixelmator for almost all my graphic design needs, but you may not need all that capability. Sometimes all you need to do is resize your image before uploading to your blog. If you're not sure why you might need to do that, here is a disambiguation for you:
In general there are two different "resizings" you can do. The first is exactly what you think it might be: changing the dimensions of an image. Here's the thing, though: if your image is from your camera, it's likely to be a very large file because it's stored in a high-pixel format. Your printer is anywhere from 300–1200 dots per inch (dpi), and that's what you want if you're printing your photos for your Aunt Sally.
However, your computer screen is 72 dpi. That's the resizing you want to take care to make if, like me, you're uploading your images directly to a server for use on your blog or whatever. Yes, your blog software will display your 5MB image at 72 dpi, but your storage is still sucking up 5MB because all the little pixels are still there. Resizing your pixel depth can take your image from 5MB to 150KB. That adds up.
Therefore, sites like Resize My Image are just the thing you need. (This one also allows you to crop and rotate, change formats, etc.)