If you need to hire a lot of employees in a short period of time and still don't have a full-service HR department in place, you'll need to decide whether you want to work with multiple agencies and contingency firms at once, or depend on one to work hard for you.
Some firms get excellent results from developing deep relationships with one (or two) agencies, while others get a lot of people hired quickly by using multiple firms. In general, deeper relationships with fewer firms make the most sense, but most firms don't cover all talent areas.
Typically, you'll find firms that specialize in technical, marketing, or administrative and clerical staffing. You'll want to build relationships with each type of staffing partner. Contingency search firms do a better job of sending you qualified candidates when they've had a chance to get to know your organization, and you've take the time to explain your needs thoroughly. This can be time-consuming, but it will pay off if you're working with good search firms.
If you work indiscriminately with multiple firms, you will eventually end up with chaos. Common problems that arise from this type of confusion include recruiters sending candidates for positions you've already filled, or sending the wrong candidates because you've changed the job requirements. You might also be presented with the same candidate from multiple recruiters, since job seekers often work with more than one recriter at a time.

