Be sure to qualify the tooset you look at to be sure it will support the application you are testing. Most load test tools I found support only web (HTTP).
Here are some of the vendors I ran into:
Performant.com, Neospire.net, Radview.com, Segue.com. Empirix.com, Merc-int.com, Rational.com, Compuware.com.
Mercury Interactive looks that the market leader in both web and non-web applications, but may be a little more expensive than most.
Be sure you know what protocol you app. uses before you start talking to vendors since most load test tools record only the protocol-based conversation with the server. They do this so they can run hundreds or thousands of simulated (virtual) users at a time from a single PC.