The 4850 is the next card really up from the 4770. I would look at any GPU in the 4800 series or any 5000 series card. A good all around card with DX11 is the ATI 5770. I'm a fan of XFX cards due to their great warranties and performance.
Here is a site to look at for options.... http://www.overclockers.co.uk/productlist.php?groupid=701&catid=56edit:
G.SKILL or OCZ are both very good memory. I would go with which one is the lowest cost for you, since they both have similar timings and speeds.