GMK Dolch. Cherry profile thick doubleshot caps with very nice legends and unbeatable quality. The latest Group Buy for them has recently closed, but you could ask if anyone wants to transfer their set:
http://geekhack.org/index.php?topic=58608.0I wouldn't bother with "proper" backlit keycaps. They're all thin ABS rubbish except for the Deck set (horrible font) and the new PBT+POM Vortex set, but I'm not sure what the quality of that set will turn out like.
Background glow around nice thick high quality caps is very nice. Especially with white backlighting, IMHO. So look for a set that is high quality that appeals to you.
What keycap profile do you prefer (SA, DSA, DCS, Cherry, OEM, etc..)?