In reply to Flinticus:
As others say, Tryfan - Bristly Ridge - Glyder Fach & Fawr - Y Garn etc is an excellent round, with the option of extending to Foel Goch. Personally I've only gone as far as Y Garn (except when doing the 3000s, in the other direction).
The North ridge of Tryfan is one of the classic scrambles, good grade 1, but with ways round the hardest or most exposed bits. Bristly Ridge is, to me, slightly harder and less escapable, but fairly short. After that, the unusual rock architecture on the plateaus is fascinating, before you drop to Llyn y Cwn. Y Garn is a nice hill in its own right, with steep cwms (corries) to the east.
You can pretty much wander at will over these hills, the only bit I'm not sure on is the walled areas below Foel-Goch and NE of Y Garn.
Not sure I'd drink from the streams near Llyn y Cwn, too many folk trogging through them, and there's not a lot else until the descent.
I'd grab a copy of the 1:25000 Explorer 17, there's loads on it for future trips.
Enjoy!