You might also consider some on-demand scanners. Hitman Pro, Trend Micro HouseCall and Norton Power Eraser have good reputations for finding things other products miss. In the case of NPE, it pays to heed their warning: The tool uses more aggressive techniques, hence there is a risk that it will flag legitimate programs for removal. You should carefully review the scan results page before removing any files.
Hitman Pro 3 - SurfRight
HouseCall - Free Online Virus Scan - Trend Micro USA
Scareware Removal | Norton Power Eraser