Looking at flights out of Reykjavik tomorrow, main cities I'm seeing with multiple flights:
Frankfurt: 6:00, 7:25, 14:35 (2:35p)
Paris CDG: 6:00, 7:40, 15:20 (3:20p)
Copenhagen: 6:30, 7:45, 10:30, 13:00 (1:00p)
Amsterdam: 6:00, 7:40, 15:10 (3:10p)
London (Gatwick): 6:10, 7:45, 15:30 (3:30p)
London (Heathrow): 7:40, 16:10 (4:10p)
Oslo: 7:50, 11:40, 12:10
Helsinki: 7:30, 18:00 (6:00p)
These are just the direct flights from KEF, when looking up the departure schedule
I personally like the look of Copenhagen, but that's just me