Here are my two cents:
If you want to beef up your 510 a bit, you can't go wrong with an eGo. I enjoy mine very much.
However, if you are looking for a regular ecig that is better than a 510, I would suggest a 902. It has all the vapor of a 510, with much better taste and TH. I got one recently based on a review I read, and I've been pleasantly surprised. I've been a 510 user for a very long time, and the 902 is just better in every way except price. The atomizers can be just a little more expensive than a 510 atomizer. You can buy a 902 at ModernVapor, or Revolver has them with the name Infiniti Ion.
How is the 902 different from the 901?