If you wind up applying for full-time work, or if you're applying to some new temp agencies several months after you started, you will want to stick your temp experience on your resume. There are a couple of different ways, depending on the work you did.
If you were on long-term assignments, list the company you worked at as your employer.
Office Assistant, Big Name Client Inc.
Placement via XTREEM Staffing, January 2007 - August 2007
List of all the impressive-sounding things you did.
If you did all short-term assignments, list the agencies that gave you your most impressive ones.
Temporary Employee, XTREEM Staffing
January 2007 - present
Provided office and reception support for several companies including Big Name Client Inc., White Collar Hell, and Impressive Sounding Labs.
Mention your excellent reviews, return assignment requests, and maybe gush a little about how you demonstrated your ability to learn quickly and excel at everything. If you did jobs more specific than "office assistant," elaborate in whatever format the rest of your resume is in.
If this resume is for a new temp position, emphasize the variety of jobs you did. If it's for a permanent position, pick and choose your most relevant experience.
Thanks to this page for teaching me how to do this.