Online PC Scanning resource.

Here are a few sites which offer free Online PC scan for spy wares and other malicious content. I find it useful at times when you suspect that you are infected. In the end its the best practice to buy a anti virus package for your windows machine, this will come handy before something screw your machine.

Microsoft One care PC Scan
Symantec PC Scan (virus and online threats)
McAfee Online PC Scan
Trend Micro Online PC Scan
BitDefender Online PC Scan
Kaspersky Online PC Virus Scan
Panda Security Online PC Scan
F-Secure Online PC Scan

Online File Scanner by Kaspersky
Kaspersky Online File Scan

Free PC scan/security resources
TheFreeCountry.com