Anonymous 4 is one of the outstanding medieval ensembles in recent years. You won’t really go wrong with any of their recordings. Here is one: http://www.amazon.com/gp/product/B0000007DL/ref=as_li_qf_sp_asin_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B0000007DL&linkCode=as2&tag=thewesttrad-20
If you want the texture of male voices (Anonymous 4 is all women), Chanticleer has a CD of chant: http://www.amazon.com/gp/product/B000000SRW/ref=as_li_qf_sp_asin_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B000000SRW&linkCode=as2&tag=thewesttrad-20
If you want to try some secular music (e.g. troubadour songs) of the period, the Martin Best Ensemble is good: http://www.amazon.com/gp/product/B000QR16V4/ref=as_li_qf_sp_asin_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B000QR16V4&linkCode=as2&tag=thewesttrad-20
I believe you can sample tracks at all these links. I hope you find something you like!