I've taken it as my "job" (a purely voluntary one!) to mind this forum and
try to support the beta process. As such, I'm not the expert on other
products.
Sunbelts Counterspy product is another which is an outgrowth of Giant's
technology--Sunbelt licensed its use before Microsoft bought the company.
Microsoft is obligated to supply definitions to Sunbelt through July of 2007,
as I recall.
For removal, many folks here like Ewido. I don't know how its real-time
protection compares.
I don't believe there's anything in the "no cost" category that compares to
Microsoft Antispyware. Additionally, in comparative reviews, Microsoft
Antispyware, beta or not has come out among the top finishers.
I hope others will chime in with their favorite other products.
One other note. The final technology to grow out of this beta in addition
to being available for free in Vista, Windows XP, and I believe, Windows
2000--will be a part of two subscription products from Microsoft--Windows
OneCare Live:
http://windowsonecare.com
(a product aimed at individuals and very small businesses)
and Microsoft Client Protection
http://www.microsoft.com/windowsserversystem/solutions/security/clientprotection/default.mspx
which is aimed at large managed networks.