We've been having debates about focus groups in our office and how to balance the need for usability feedback vs. the urgency of getting a site (or microsite) live.
I found Usability First: Methods
somewhere along the line and found it pretty useful for breaking down the different types of methods.
What methods have you used successfully? Likewise, what methods have you used that you weren't satisfied with?
We've been really happy with task analysis in our office, but I have mixed feelings about paper prototyping, for example. I'll explain more in the comments when I get a chance.