Depends on what you are looking for. There are some central sites which have great content. rfactor central f.i. has some nice mods available.
Offcourse, there is still the mod section on RD. Soon, the RD Download section will return so new mods can be uploaded again, and that's obviously the best place to get your mods . In the mean time, if you look for something special it's best to ask. Google can help also, but that takes a bit of time looking into the different sites.
There are a few of these sort of sites that host a lot of stuff but now with megaupload and a few others closing down the choice is somewhat limited unless everyone reuploads mods to other hosting sites.