Also, where would I find them?
Tortoise HG. All the tortoise goodness, now for Mercurial.
UPDATE july 2020: The original official website linked above is abandoned.
The project moved to: https://foss.heptapod.net/mercurial/tortoisehg/thg
GUI clients & Other tools: https://www.mercurial-scm.org/wiki/OtherTools
If you're using eclipse:
http://bitbucket.org/mercurialeclipse/main
If you're an OS X user, Murky is pretty decent.