HijackThis freeware by Trend Micro
This is a very powerful cleaning utility that creates a list of items loading in your system and gives you a means to remove them. A fair amount of knowledge and willingness to research the entries is required to use this tool effectively. Originally created by Merijn.org

Warning: It’s possible to remove the wrong thing and damage your system, so I only recommend this utility for experienced users. Hijack This has a logging ability that is often used on message boards and support forums to let the community help analyze an infected computer.