Hi ste.sho and welcome to the forum. Lots of helpful peeps on here. A lot will depend on what you want to spend. The logical step up from a 510 would be an ego type battery because that gives you more battery life and options to try the growing variety of 'mizers' on it. The more mAh the longer you get between charges.
I assume your 510 kit uses cartomisers? How do you get on with it?
More oomph you say, well get on to variable voltage this will give you a bit more oomph now what sort of size you can go for an ego VV or Vamo/LT style and then tou got to decide what you want to have on top, you can go Clearomizer CE4/5, nova tank or go for a rebuildable.
There are so many configurations but you need to think what would suit you and your tastes but the move from 510 to VV is going to blow you away
One of the best new clearomisers on the scene is called the Evod. This vendor is now carrying a kit. It's not the cheapest but you do get two batteries and two evods plus charger plus 5 spare heads. This would last you quite a while. Just add juice! http://www.vapeescape.co.uk/evod-650-starter-kit~504
I've been Vaping for nearly three years and tried a lot of different and expensive kit but I like these a lot. All about opinion at the end of the day though.
Sorry ste.sho it can be daunting but have a look around the forum and don't be afraid to ask questions.
Check the vamo and look at videos see if this is the sort of device you would feel comfortable with or the Ego batteries as these would be a good step up.