You should PM NathanJD, he's just got himself his first R2a after having Zorki's and has been in the same situation, though I think he has a 50mm Jupiter already.
I suggested to him an old Canon 35mm 2.8 LTM if you can find one as they're cracking little lenses IMO....having had one before buying a 35mm Summicron v4.
I'd also recommend the Canon 50mm 1.8 if your budget covers it, a great cheap lens...again one I had and am very happy with, I still use it alongside my CZ 50mm f2 Planar.
You'll get loads of good advice from people that have had far more experience with different lenses than I have but eventually it'll be bite the bullet time and you'll have to take the plunge with one of them without having used it before. Unless someone is willing to let you borrow one for a while.
Where are you based?