If I'm cleaning up a box I usuually use a combination of Ad-Aware and Spybot, run from a BartPE CD(http://www.nu2.nu/pebuilder). Then use Trend Micro's online AV scanner while booted into the OS.
Not a dedicated online anti spy/adware....although some of the better online antivirus scanners are getting good in this area..such as Kaspersky and Trend Micro, I think BitDefender has one too.
For local installs...I've found SuperAntispyware to be the best. Free...constant updates, very good detection and removal. Still use Spybot S&D. Grisofts AVG AS is quite good. Pretty much stopped using Adaware and Microsofts AS/Defender...I find them quite useless.