well, first off I would suggest checking out anything by lovespiralsdownwards. they aren't exactly instrumental, but the vocals aren't so dominating in the music. very ethereal.
may sound cheesy, but just some regualr mood music such as background noises(those cheese cd's you see at stores, i.e. sounds of the ocean...). or you can get some lounge, downtempo, some deep sexy house.
those are just some genres for you to check out. mind you, these genres aren't of the mainstream entity, so you will hafta do some homework and search. but when you do find something, you will appreciate your findings... I don't know any off hand, but if I find any, I will post on this thread