Two quick notes:
First, you really want a long-term support release. Your main options here
are Debian and spinoffs (Ubuntu LTS, for example) and RedHat Enterprise and
spinoffs (CentOS, Scientific Linux, etc). If you know one of these groups
go with it.
Second, GUI's usually come separate from the distro. You can choose GNOME,
KDE, XFCE, etc. depending on your taste. Really the best way to go is to
try a bunch out and see what you like.
If you are doing development, you want a cutting-edge distros (so something
like Debian Testing, Ubuntu, or Fedora).
Best Wishes,
Chris Travers