There are minimap mods that are allowed. Make sure you check to see which ones are though, don't want to be accidentally banned because you were using an illegal mod.
I discussed this in the VIP section. The problem with it, is that is sucks up a lot of server memory because .PNG files have to be made for ever inch of map that is explored. 11 gigs worth of map is a lot for a server to process and handle.
Yeah, it ended up completely filling the SSD with png files the last time I tried it. Unfortunately, that is one of the downsides with having our truly unlimited maps - you can't map 'em!
1.6 will bring the local maps though, which should at least partially fill that hole.
josh500 - there are a few allowed mods, including Zen's mod (which has a built-in map). We generally disallow map mods, since they can help a player cheat, but Zen's mod isn't like that.
Yes PD, those mods are fine as well. Texture packs/mods are fine as long as they don't make any currently opaque blocks transparent or semi-transparent.