Well hatfarm's been hard at work over at http://www.stonepool.com/xcom/ on his Windows-based X-COM editor and it's just been ported to Terror from the Deep, so head on over there and download it!
If you feel like helping decipher some X-COM code in the interests of mod-making then head on into the X-COM Modders forum and read up on the latest documents and tools.
Another popular tool that's recently been updated to version 9.6 is Scott T Jones' XcomUtil - whilst this is only a Beta at the moment, it contains new versions of the farm and desert terrains and contains a terrain editor!
In other news I feel I should apologise for this news being a little out of date in some cases as a lot of my time has been spent on a rather large project that we're hoping to unveil by the end of September/early October all being well. After that the news around here will be very much more lively and there will be a lot more to do and see. Keep your eyes peeled (not literally) for updates this month