It is hard to say that one AV, Trojan scanner, etc. is best, because there is not one that will detect all problems.

Some tips here:

You might consider installing Mozilla / Firefox.

Spyware detection and removal programs:
You may also want to consider installing either or both of AdAware (free version) and Spybot S&D (freeware). Use these programs to regularly scan your system for and remove many forms of spyware/malware.
a. AdAware:
b. SpyBot S&D:
Check for updates in Adaware frequently.
I would check for updates in SpyBot once a week or so.
I scan with each at least weekly.

Trojan scaners, to name a few:
TDS-3 /DiamondCS ** Download & install the 30 day free trial, update it manually as described here: as the trial version doesn't have auto update enabled so you will have to do the update manually.
The automatic update only works with the registered version which costs $49.

A2 squared free Trojan scanner:

TrojanHunter: Also has a free trial version.

The Cleaner:
The Cleaner is free for 30 days

There are also various online Trojan scanners:

Also, the following free programs:
a. SpywareBlaster:
b. SpywareGuard:
Periodically check for updates.