In reply to climbercool:
The area around vang vieng is gorgeous, the actual town is mehh to be honest. There's one true climbers place there set up by a western guy, called 'Adam's climbing school' (
http://www.laos-climbing.com/ ) they have guides etc but renting gear is pretty expensive. Take your own gear if you can.
I'm assuming while staying in Thakek you've already found this place:
http://greenclimbershome.com/
Sorry can't say I know more places in Laos to climb, although that doesn't mean there aren't more! I'd suggest emailing the people from one of these companies for advice
I did a bit in Kampot (which is beautiful) in Cambodia and these guys are extraordinarily helpful with superb local guides who they trained up to climb and lead belay, truly nice people:
http://www.climbodia.com/