Like Train2 , I can recommend the Innokin iTaste MVP2. It'll give you a little more flexibility with variable voltage/wattage, the battery life is great, and I haven't really heard any complaints about the device yet. I haven't used one, but I have a few friends that have and really enjoy them. I've got the step up from the that that Innokin carries, the VTR, and I'm quite happy with it. It even comes with eGo threading, so you can use all your eGo tanks, or if you want to use your ProTank, you can slap on your beauty ring and you're ready to go. It won't break your bank, either!
I've heard a lot and seen a lot of reviews about the Eleaf iStick. I haven't used one or seen one in person, but there's a lot of hype out there about it right now. It's in the same price range as the MVP2, too. It does give you a greater range of wattage and voltage than the MVP. On the iStick the max wattage is 20w, and the max voltage is 5.5 volts; the MVP has a max wattage of 11w and goes up 5.0 volts. I have seen that because of way the current runs through the iStick, it tends to run just a bit hotter on average than the wattage/voltage than is listed on the device, just something to keep in mind.
Below are some reviews from RubyRoo on YouTube on both products. She does really great reviews that aren't overly complicated, and she tells you exactly how it is. She isn't afraid to discuss negative aspects of a product at all!
Innokin MVP 2.0 Review
Eleaf iStick Review