What Windows services can I safely disable?

I’m trying to improve the boot time and general performance of a Windows XP machine and figure the massive collection of services that Windows automatically starts have to have an impact. Are there any services that I can safely disable? If so what are they?

Obviously the services are there for a reason, so when listing a service, please provide reasoning & examples of when you’d not disable it.

Solution:

Black Viper maintains what is considered by many the definitive guide to Windows services.

http://www.blackviper.com/category/guides/service-configurations/