A couple of years ago I built an arcade cabinet, thinking mostly of using an XBox. I was going to use original XBox controllers for the job, but I ended up using 2 mad catz PS2 controllers. You can buy those controllers cheap (7.99), and in most cases, they are easier to solder than an XBox controller. The main advantage is that you can use converters for a lot of different consoles. I have 2 Madrics converters with outputs for XBox, Game Cube and PC, and another converter for Dreamcast. This way I can have XBox, PS1, PS2, Game Cube, Dreamcast and PC on my arcade cabinet. And there's a lot more converters for the PS2 controller (Saturn, PS3, XBox360). Just be careful about cheap converters, because they can be quite laggy.