This will help you understand what you need: Black Viper’s Windows 7 Service Pack 1 Service Configurations | Black Viper's Website | www.blackviper.com
Problem is, everybody is different: do you have network set up you need to access? Do you have wireless printer? I mean the list can go on and on. I have some services set to manual, so they start up when needed, but there is always some issues, when the program doesn't work due to services it needs not running, so it could take some trial and error. Also, most services are not taking much space and even when running, but not used at the moment, they could be offloaded to HDD. Personally I'm more concerned with this idiotic programs that load up at start up, even if you don't use the program at all, checking for updates and other nonsense. For example MS office, Open Office, whole bunch of other programs have loaders running all the time, they supposed to speed up start up of actual program, but the problem is they save couple seconds here, but delay boot up every time and if you run Office once a month, where is the advantage?