http://www.auran.com/TRS2004/DLS.php
there you go,look for the words Download Station towards the top of the screen,and there ya go
It also depends on what your intrested in, If you like Amtrak stuff,I'm sure Corey's site will have the stuff for you http://www.freewebs.com/virtual-beech-grove If you like commuter sites,click the picture below this,and if you like freight go to www.rrmods.com
http://www.auran.com/TRS2004/fansites_f.php has a useful list of Trainz fansites, many of which offer some freeware. Some of those sites might no longer be operational though.