Alex,
I can echo Nick's recommendation of Zion Train.They have a number of excellent albums available,some of which are purely instrumental,drifty dub - particularly good is "Natural Wonders of the World in Dub".
If you want something a bit more lively,"Homegrown Fantasy" and "Grow Together" are both worth investigating,although they are not "traditional" reggae - more "new age" reggae,if there is such a thing.
You can investigate further by visiting :
[URL=http://www.wobblyweb.com/]
where you can also download 2 excellent samplers if you have the technology.
One of my favourites from this label is Marineville's "Redpath House",again completely instrumental,but really spacey,and almost jazzy in parts (Bitch's Brew jazzy rather than three guys noodling away incosequentially).
Good luck,
Shazbut