The best "L" lens for the buck I think would be the 200mm 2.8 black beauty.
For non L lenses that will fit crop and FF, there's a few....
50mm 1.8 (of course)
50mm 2.5 CM (best edge to edge sharpness of all the 50s and $250.00)
85mm 1.8 & 100mm 2.0 (two great portrait lenses at a sweet price)
100mm 2.8 macro
For EF-S lenses for crop only...
60mm 2.8 macro (outstanding sharpness plus a macro at a great price)