Modding community - no, mainly because the source code hasn't been released yet. There are however lots of models/textures/entities/segments/etc. available, some for free, others you have to pay for. Most of the X9 ones are compatible with X10...
Cosmic Prophet's Sci fi packs are great freebies you can find on the forums (I don't have the link but it'll show up in a quick search).
fpsfree.com also has lots of good media
You can also get lots of media in the community forum, fpsc-online.com There's free media available there and there's also an online store so you can check both