Network load test equipment

[Greg Schwimer <gschwim () gmail com>]

I'm looking for equipment that can be used to load test network equipment
such as switches, routers, firewall, and load balancers with pre-defined
traffic patterns at differing rates.  Ideally, this is only something I
think I'll need 2-3x a year, so purchasing is not necessarily justifiable.
I'd prefer to rent.  What products have you used?  Where did you get them
from?

I need to be able to run pre-defined traffic patterns at various rates, in
excess of 10Gbps in most cases.

Thanks!
Greg