You'd have to pay $500-1K for these lenses, but they'd be worth it:
Contax 85mm Planar f1.4 - I'd have to dig around in my archives at home to see if/where I put the images I shot with this on my 5D (some of which showed my ex, which is why I might not still have them).
Contax 35mm Distagon F1.4 - It's a big honkin' lens, with an equal price tag, but it is truly legendary. Well worth the cash.
Contax 28mm Distagon F2 - 'nuff said.
Another lens maybe not quite so pricey as the first few, but still not cheap would be the Contax 25mm Distagon F2.8.
More important even than what lens you put in front of the camera is the mount adapter you use to put them on it. Don't stint and think you can get away with a cheap (~$100) adapter. I had one and it damn near got stuck permanently on my camera and/or the lens! I did get it off the camera body but almost broke something on the focusing screen retaining clip in the process. Spend the money for a good adapter before you go glass hunting.