Probably one of the more prolific customizers is FrenzyRumble whose paint jobs can almost look as good as their CGI counterpart as you can see with Megatron and Optimus Prime (click links for gallery). His work isn't limited to just those two. His website includes many more customizations such as Shockwave (base toy familiar but blanking on line), Galvatron, the Protectobots, and many more. I would post a few more pics and links but his flash only website doesn't make linkage impossible so instead click here to check out his work. A Peaugh video review of his work for Powerglide is below.
An example of from scratch work is MMC-01 Knight Morpher Commander that is based on IDW's Hearts of Steel miniseries from 2006 that re-imagined the Transformers as coming to Earth during the Industrial Revolution. Optimus Prime's alt mode was a locomotive and as you can the result is a pretty sweet looking design that I posted about early this year. Now that custom design is getting produced on a scale so that a Transfan can own for around $80 US. The picture to the left is a prototype picture but the final version is expected to be assembled and fully painted Transformable figure that is estimated to be released in October. To view the full gallery, click here.
Part 1 | Part 2