At first I was completely sold on the K545 but now I must consider the competition. The K545 looks to have average isolation, and may have seal problems. Seal problems are the absolute worse.
I'm still considering the MomentumOn-Ear (since it's so small! and looks so good), and HP50. I know the HP50 and K545 will sound the best but I'll give up a tiny bit of SQ for convenience (since that's the reason we use portable cans in the first place).
I think the K545's isolation is pretty good. At work, I could barely hear the phone on my desk ringing. And I listen at a fairly sane volume. I guess the seal is dependent on the individual, but the fact that you can adjust the cups and that they stay where you put them help with the seal tremendously.