Some will clean, others will warn you of an infection. Of course part of this is for advertising their products, but the scans are free. Kaspersky IMO is the best, but does not clean, however the scan log will show you the path of the infected file(s) - and ones that are locked from the scanner (some of these a legitimate windows files, others may be malware - the secret is the filename and path). Bitdefender will clean in my experience, and produces a log too. Trendmicro is not as good as it used to be, and some users have problems with crashes - TBH I haven't used it for a while
Really they are for a second opinion, as any Av is only as good as its signatures, and they can put ones mind at ease. Also it is possible for false positives to occur with any scanner.
For anti-spyware scanner only you could try this:
http://www.ewido.net/en/onlinescan/