as good as the GTX 260 mentioned WAS
I went from a GTX 260 to a GTX 560, which more than adequately serves my needs and will likely not need upgrading for a few years yet.
However, bak to the OP....
As others have said, building your own will result in getting more of what you want, rather than what you're given in a pre-build. You can select your own parts and achieve something more powerful for less cash up front. Furthermore, if you go with AMD for your CPU, the money you save over a similarly rated Intel chip would allow for a pretty decent SSD for the OS installation.
Oh, and if you're not too confident building your own PC, try around your local independent PC stores and get some quotes. I've found that the smaller independents are usually pretty good on parts and labour prices, so yeah, check 'em out before committing yourself to a major brand/company that locks you in to an arrangement with a less than satisfactory PC. In some cases, a smaller independent will take your own parts and assemble for you, so there are options open to you.
All the best with it.