Sometimes it is good to get a second opinion, especially in the case of viruses, malware, spyware, and all the other garbage you can pick up. Below are some links to some of the more populare online and free virus scanners:
ESET Online Scanner
Virscan.org - a bit different in that it allows you to upload a file (up to 20 MB) and then have it scanned by 30+ ant-virus/spyware/malware/etc. programs.
I will add more as I use them myself. For my main anti-virus program I use the free Avast resident scanner. You can download it here.