A mini carabiner works well for a keychain. I like to have keychain "babies' that have groups of keys that are used together but not very often. When I need that group I add it to my keychain cluster with the D-ring. When I'm not using them I don't carry around the extra keys. My motorcycle keys are one of those groups. My keys to my parent's house and friends's house up in Wisconsin are another. My wife goes so far as to remove her auto keys from the ring as she almost never drives. With this system one basically only carries their house keys they use every day and the ring of keys never becomes excessive.

Another method is the keychain quick-release system which is handy if you only have two clusters but if you have more groups than that the quick-release bits end up taking up nearly as much room on your keychain as one is saving. I currently use one of these quick-releases to connect the motorcycle ignition key to the rest of the motorcycle cluster -but use the D-ring system to attach that to my main keyring.