I love me some comics fan art, and here's some awesome examples:
Caleb over at Every Day is Like Wednesday sometimes puts a web comic up on his blog. Here's his "The Showcase Presents: Justice League" series, which is quite amusing, especially when Batman shows up and punches people in the head and J'onn J'onzz keeps reminding Jonah Hex that the JLA Satellite is a non-smoking facilty. (And who knew that J'onn's laser vision went "PYEW PYEW!"?)
Every now and then, SallyP treats us with a drawing of hers, and wow was I happy to see one featuring my favorite Martian! Not only it's J'onn's (and Guy's) expression priceless, but the shading is so, so lovely. Definitely check it out!
And, last but not least, Eyz from G33K Life has an ongoing "Superbuddies" strip which is based on the JLI years. (Plus some other strips, too!) Booster and Beetle are always up to something, and J'onn's Oreo addiction gets him into his fair share of (hilarious!) trouble.
Have fun and to all you artists out there, keep drawing!