Also you'll have to provide much more information:
budget (even if only estimated)
indoor/outdoor
support lighting or not
expected rough distances you'll be shooting over
any plans to upgrade to fullframe
etc...
The more details the better otherwise you'll just get recommendations for every lens between 50mm and 200mm
As overread said, but in general any 50mm fast lens will be nice on the 7d. Examples Canon EF 50mm f/1.8, or better EF 50mm f/1.4. Sigma have a well regarded 50mm f1.4 also. I really like the canon EF 85mm f1.8 but you do have to have room to use this as you will be quite a distance from your subject