I came upon a really amazing site one day that sparked retro joy in my retro heart. Its called MUSHROOM-KINGDOM.COM and its got some rather cool features. The coolest part of this site is its "Mushdraw" tool that lets you create custom Mario mushrooms. Its got some R-B-G sliders for different aspects of the mushroom so you can make any crazy combination of colors you want.
Once you make your mush-masterpiece it gets saved in the Mush-bank where other people can view it and vote on it.
You'll be amazed how much time you can lose playing with this. It's actually extremely addictive. And as an added bonus, you can click on the music box and turn on Mush-radio while you play. Mush-radio is a little music player that has a collection of Mario tunes.
All in all its a nifty little site. Check it out!