StartupControlCenter.  You can end up with many things autorunning from the startup folder or from the registry.  This utility gives you quick access to all such areas so you can take control, delete undesirable items, or just disable them if you wish.
http://www.sureshotsoftware.com/products.html

WhatsRunning.  A very deep look into all the stuff running on your pc, and I mean deep.  It can be daunting when you view it - what does it all mean?  But you'll find you'll need it for looking into certain areas sometimes, such as finding out exactly which programs are connecting to the internet, what's using up your pcs processor time etc.  There are some tools that just let you see the summary, but its a good idea to have one like this that goes all the way in - and you only need to go as deep as you need to.
http://www.whatsrunning.net/whatsrunning/main.aspx

JPG Scanner.  Probably not as widely known as it should be, it is a fact that among all standard image file types, the JPG is the one that can contain a virus.  Such a virus can be activated simply by viewing the picture.  This tool scans one or more pictures and tells you if they contain a virus.
http://www.diamondcs.com.au/jpegscan/

JPG Cleaner.  A good tool to use with the above one, this strips out completely the section that can contain a virus (such a section is not needed in the picture and the picture will behave fine without it.  In fact you may be surprised just how much smaller the file size becomes).
http://www.rainbow-software.org/programs.html