One of my favorites right now is the Rogue RDA. Easy to build on (dual/single coils), adjustable air flow, small form factor, great flavor... The best part is the air flow comes from the top so it is highly resistant to leaking. I use it on both my iStick and mech mods. I never have to worry when I put it in my pocket or having to hold it a certain way.
You can get the authentic but there are several clones available. I will be picking up a second one in the near future.