We don't have a bunch of requests in yet but I'll poll the admins when I'm in the server.
Off the top of my head a coordinate mod would be good. Something to tell you where you are so other people can find you and your builds in a big freebuild server. I figure this one could probably be made in 10 minutes.
We're also looking to make a contest mod for build contents but that's a big one. I'm thinking that there should be some kind of mailbox brick or something, and when you place it it registers it's location and the person who built it. Then judges or just other players can come around and leave feedback and a rating, and it's all tallied up and viewable through some command. A goto mailbox command would be good for finding builds in general, even without a contest. KINEX was looking into one for the SS server at one point (maybe they did make one, I don't remember), so he'd probably have some more suggestions. I'd probably be willing to put a cash bounty on this one depending on the quality and how many of the features are met. Some kind of cute mailbox brick where players can only place one and that makes it really simple to register your build is probably my biggest desire out of this mod.
Some admin utilities, like force trust would be nice. We found that a lot of existing server mods were either bad or didn't fit our needs so slick's been rewriting some of them into a general server plugin.
A way to move people's builds around would be nice too.