Hey kids, depends on how 'ambient' you wanna take it... do you mean pure ambient? as in... soundscapes without any beats whatsoever? or beat ambient/downtempo, which has beats, but is still relaxing and texturey? do you want it really danceable? kinda danceable? or not danceable at all and basically is being played to a room fulla vegetating drugged people. (IE the local seniors centre, they love ambient.)
check out people from the labels of Force Tracks, Force Inc, Mille Plateaux, Kitty Yo, Rephlex, Mole Listening Pearls.... thats a start for you. from there you can probably refine your idea of what 'ambient' means to you and build up a record collection surrounding that sound which to you, means 'ambient'. but it's different for everybody.
cheers and let me know what kinds of goodies you find, (artists, tracks, labels)