Gotoh 510's are awesome tuners, and come in several colors and styles.
http://www.stewmac.com/SiteSearch/?s...20and%20tuners
You could also just replace the buttons themselves, leaving the existing machines in place.
The two things to watch out for are where the anchor pin is located (6 o'clock, 9 o'clock) and the diameter of the posts (whether or not you need a bushing to fill in a gap for a larger hole).