Depends a lot about how much walking you're willing to do, as you'll get some great vistas from walking up a couple of mountains, and its all very weather dependent there.
Cwm Idwal is a good place to visit, fairly easy to get to, gentle walk up to the lake, and you can get great views down Nant Ffrancon. If you want an elevated view of Llyn Idwal, then follow the path around the lake which climbs at the furthest point (with the option to climb up past Devil's Kitchen if you want to climb well above the lakes and get a view in the direction of Snowdon).
Not uploaded any recent photos
Coastal wise, travel to Anglesey to Llanddwyn beach, parking costs either £3 or £4 (there's a toll-gate), its a lovely long beach, with an interesting island on the end of it. If the weather's nice try to time your visit with the sun setting, as the sea tends to get very calm, and you get great views towards the mountains of Snowdonia, and the Lleyn Peninsula.
As said before Rory has some great photos, but perhaps from less well-trodden areas, which may be harder for you to find not being familiar with N Wales.