The Internet Archive added a whopping 2,311 old DOS games to its archive! All games are playable via in-browser DOSBox-based emulation, without requiring the installation of special plug-ins.
You can give it a try over here. The list contains many popular games including Duke Nukem 3D, Stunts, Lemmings, Street Fighter II, Dune 2, Aladdin, The Lion King, Leisure Suit Larry, Zelda, Scorched Earth, Prince of Persia, etc.
Several of the games I tried didn't work too well but it's a great trip down memory lane!