I bought the Vivitar 55mm f2.8, in Canon FD mount, after Vitaliy advised it. I can't complain, fun lens to play with, and cheap (got mine for 70€, some here got it cheaper with different mount).
Another lens I bought (also advised by Vitaliy... I clearly lack personality) is the Canon fd 80-200 L. I love this one, and it has a 1:3.1 max magnification ratio, which can do some very nice macro when used with ETC. Again, quite cheap, around 130€ (I bought a 2d one this week for 90€, maybe a Xmas gift for a friend)