In reply to Chris Matthews: A few good climbs on Idwal slabs as you suggested, yet it's quite popualar and the way off can get the unwary lost. Although it's a staedy, shortish walk in. A link up of Tennis Shoe, Lazarus, and Groove Above would give a full day out. If you set out early and do those in quick time, you could get maybe sqeeuze in Cental Arete on Glyder Fawr.
Tryfan Bach next to Tryfan has loads of good 2 pitch routes Diff-Sev.10-15m walk in. Usually has 2 or 3 groups, but is never crowded as theres plenty of room. A fun, full day to had there.
AS mentioned East face of Tryfan for some good mountaineering routes. Grooved Arete, Gashed Crag are 3 star routes, plus many others if they are busy.
Clogwyn Bochlwyd, west of Tryfan has some good single/multi-pitch D-VS.