Linking to a site that has a clearly stated goal of offering games that are not subject to copyright law, or have had their copyright waved by the author, is allowed so long as they don't BLATANTLY appear to be hosting known copyrighted material.. i.e Youtube has tons of stuff not subjected to copyright but can't police copyrighted content that comes up until they are notified, and because of the sheer amount of users uploading stuff.
So just like we don't have a problem with Youtube, I think it is safe to say we don't have a problem with free sites, that do not appear to be hosting blatantly illegal software.
But a warning to anyone who read this.. This statement is not a license to slap any old link up on the forums. Having one or two copyright free pieces of software on a site otherwise hosting illegal content does NOT qualify as a valid link within the Forum Rules and we will not tolerate anyone splitting hairs or pushing the limit with their linkage. You will be disciplined harshly, including the possibility of instant long period bans for standing members who should know better. And remember the linking to a site that links to rom distributers factor IS in effect and enforced at Moderator or Admin discretion.
That being said, everyone feel free to share links like Thanameless has posted.