Don't forget about all the abandonware sites, too. Abandonia and Home of the Underdogs are pretty great.
Yeah, but those are a bit legally iffy quite often, if you mind that kind of thing.
Abandonia is completely legal, afaik. There's tons of old games you can't get there because it would be, like you say, legally iffy.
I absolutely adore Abandonia, but I'm afraid I have to correct this misconception. Abandonia is only as legal as abandonware in general. Strictly speaking, abandonware is not by default part of the public domain, as the length of copyright in most, if not all countries is longer than the video games being shared have been in existence. The only reason abandonware is permitted to exist is because most of the copyright holders are unable or unwilling to defend their copyrights on games as old as these, but as long as you live in a Berne Convention signatory or the United States, violation of copyright is still technically illegal even if no one does anything about it. Hence, "legally iffy". I have no idea where the archive.org collection falls, but unless they received permission from every single company on the list (many of which no longer exist), I would be astounded if they were also perfectly legal.
That said, Abandonia is rather good about taking down games after receiving C&D orders or if they're made available for sale again, so they are a good option. And abandonware in general is safe from legal retaliation, both because many of the copyright holders are defunct or vanished and because of the not entirely unwarranted perception that there's not much money in it.