1- Carneddau from the Gerlan side, either an ascent of Carnedd Llewelyn using the Caseg Valley, or climbing the shoulder of Bera Mawr and Yr Aryg, to reach the Central Ridge.
2- A circuit of the Southern Rhinogs, but heading in a anticlockwise direction from Bwlch Y Rhiwgyr, Diffwys, and onto Yr Lether and ending up on the summit of Moelfre.
That one is pretty magical, and your virtually guaranteed peace and solitude.
Also visiting Bryn Cader Fanner stone circle above Talysarnau, also part of the Rhinogs.
3- An ascent of Cader Idris, using either the Minnfordd path or Foxes route, either way is a classic.