I have a Macbook Pro Early 2011, Quad Core i7 processor with Corsair 8GB of RAM DDR3 1333MHz, OCZ Vertex3 SSD 120GB and HDD 500GB configuration. Pre-installed with Mountain Lion. But, you need to use your own Apple ID to upgrade the Mountain Lion.

It's well-maintained and still running fine.

I could preconfigure the software inside, tailor made for software development (installing Xcode, homebrew, ruby, python, etc.), or I could just clean up everything and make it brand new for general usage.

I also have the original SuperDrive if you need it, but there's no enclosure for it.