Software Development Process for a small team?

I work for a very (and I mean very) small web development team. The team consists of, A designer, A sales guy, a programmer, and a project manager.

I’m looking for a software development process that will work best for us. I’ve read about a few of them but they all seem geared towards teams of a larger size.

Does anyone have any suggestions on what we can use to help our process along?

Thank you!