<p>What are your best usability testing tips? 
I need quick &amp; cheap. </p>

You have to watch people use your application. If you work in a reasonable sized company, do some 'hallway testing'. Pull someone who is walking past your door into the room and say something like, 'Could you please run the payroll on this system for the next month? It should only take two minutes'.
Hopefully they won't have any problems and it shouldn't be too much of an imposition on the people walking past. Fix up any hiccups or smooth over any processes that are unnecessarily complex and repeat. A lot.
Also, make sure you know what usability is and how to achieve it. If you haven't already, check out
The Design of Everyday Things
.