Here are a couple links to help you decide:
Disable unwanted services and speed up Windows
Services - Start or Disable - Windows 7 Help Forums
One thing to remember, if you try to make changes, do a restore point BEFORE setting off on your adventure, then try stopping each one to see what happens. If things go wrong and your PC locks up you can always restart it to get back to normal use.
There is one (actually a few) named "Service Host" that can mask all sorts of things and have viruses or malware inside and they are hard to pier into as they will have dozens of DLLs and other parts. There are utilities that allow you to view their internals so try them also.