10-8 Performance has a new thumb safety available. CNC machined from heat treated steel with a serrated thumb pad, 10-8 Performance describes it as "...absolutely straight, and all the contours are cleanly machined. The lever is just the right width for easy manipulation, yet it is narrow enough not to get in the way....This thumb safety is superior to any cast or MIM safety that you will find on factory 1911s..." It has a serrated thumb pad for positive purchase and a straight parallel shaft. Currently available in blued carbon steel and glass bead blast stainless, it will be available in carbon steel shortly.It is not available in an ambidextrous version, nor will it be any time soon. If you're looking for an ambi, the HMFIC at 10-8 Performance recommends the Wilson Combat Bulletproof ambi.
This isn't a review. I've never used any of 10-8 Performance's stuff, although it's spoken of very highly by several individual's I hold in great respect. I just know there are a lot of 1911 shooters on here and thought I'd pass it along.
Available at http://www.10-8performance.com/1911-thumb-safety/