So I find myself working for a few weeks in a small team of four, including me. Quite a change from my last job at a 300+ developer shop where I'd been part of the adoption of an agile methodology.
I've been sneakily introducing useful tools like a continuous integration server and am surreptitiously starting test-driven development.
What other agile project management and development practices are appropriate for the smaller shop?
Communal code-review whether or not everyone is on the same site
I think you may want to flip the question around; what agile methods would not be suitable because you are a small team. I am no expert in agile practices, but I can't really think of any that would not be appropriate because of your team size.
IMHO all of the development practices are appropriate. In fact, for a long time an agile team was expected to be a small teams (5-9 people). There is an artile of infoq about it.
Also, because you have a small team both communication and collaboration will become easier, so the practices would work even better.
Well, to me, your actual configuration is much more appropriated for Agile than a 300+ developer shop (not really sure how Agile was implemented there, I'd love to hear more about that as scaling to that size requires a very high level of maturity on Agile IMO).
So, my answer would actually be: starting with 4 people, all values and practices are appropriate and valuable. Actually, what Agile methodology did you adopt previously? What practices did you implement? What makes you think they wouldn't be appropriate?
PS: If I may, try to see beyond engineering practices, Agile is not (just) about that (this is especially true for Scrum). Practices such as Test Driven Development, Continuous Integration, etc are nice but they are just a mean, not an end. They won't suffice for a successful Agile implementation. Agile is a business oriented organizational pattern. In other words, technical stuff is not really the best starting point when implementing Scrum, you should start with organizational things.
Focus on introducing practices that add the most value to the team.
As the team is small impact of the change will be highly visible, if you work with the team and show improvements then you can go back and add another one - again the one that add the most value to the team.
One of the most important thing is that the projects are approached with an agile mindset, adding tools & techniques in the context of long projects that can't adapt to change & are not highly tuned with the customer won't have the ultimate result that you should be aiming for.