I'm going to chime in with another recommendation for the KR808D-1.
It is a two piece design - battery and cartomizer. The atomizer is built right into the cartridge, so each new cartridge is a fresh atomizer - no mixing of flavors, no replacing atomizers, just screw on the cartomizer and go. When it's empty, just toss it and put on a new one. You can even refill them, if you want to go that route, but many don't.
They are probably the easiest way to get started on e-cigs, they require a minimum of fussing, and there are lots of suppliers out there, with a wide variety of flavors, battery sizes and colors, lots of options.
My supplier is in my sig - give them a glance if you haven't ordered anything yet, and do a search for "cartomizers" - you'll find lots of others as well.