ACCustomFigures.com is a site that's been on my radar for a few years now. AC is an amazing action figure customizer that makes wonderfully constructed and cleanly painted figures that fit perfectly into existing toy lines. He makes Marvel Legend and DC Universe Classics figures that look better than what you'll find on toy shelves. Luckily for us that don't have his talent, he takes commissions and occasionally sells customs on ebay.
About AC Custom Figures:
Here are some samples of AC's action figure customs: