While it's generally not recommended procedure if you don't know what you're doing, you can use
Lingon to manage launchd services. You can also use launchctl for a command line version that's bundled with OS X.
WARNING: You should be well advised that you can mess up Mac OS X if you disable the wrong things, so please be very frugal with what you disable. In fact, I would
not recommend this for most home users, as it's simply not necessary and potentially disastrous. So please consider why you feel you may want to manually control a service, as it's likely the reason is moot.
Services aren't usually "always running," because launchd will dynamically start them upon request. Meaning, for example, once an ssh request comes in, if the sshd service is enabled, it will startup sshd and not before.