For platformers, you can't go wrong with...

Iji
La-Mulana (original version)
Hurrican (Based on the Turrican series)
Spelunky

Considering the state of our wallets lately, this thread ought to be necro'd.

Someone already mentioned Battle for Wesnoth and Warzone 2100, and someone else already mentioned Yume Nikki. All three would be first on this list o' mine.

But here goes:

Transcendence: Star Control 2's Melee combat meets Wing Commander Privateer... With maybe some tampering by the likes of Loki or Tzeentch. The game is a pretty small file that lets you do business, kill enemies, and/or die in horrible ways while making you fly in a linear secession of stargates. There's a Mod that came out recently (the Network) that lets you take a much more varied path through the stars, but this is a game you shouldn't miss.

http://www.neurohack.com/transcendence/

Visions and Voices: If RPG Maker was a swamp, this game would be one of the few beautiful flowers that grow in it, and unlike classics like To the Moon and Defender's Quest, this game is free. It's what would happen if survival horror met RPG (with actual 'run for your life' kind of horror instead of Koudelka's atmosphere). You have to conserve your food and supplies, but the rewards are great. Scour a ruined village, recruit survivors, and fight for your very life.

http://rpgmaker.net/games/1212/

Vega Strike: You're talking to a Freespace and Wing Commander fan, so here you go. A free space sim.

http://vegastrike.sourceforge.net/

Some good old and classic style JRPGs:

Monster RPG 2 in and [url=http://www.desura.com/games/monster-rpg-2]Desura.

One Night in IndieDB.

One Night 2: The Beyond in and [url=http://rpgmaker.net/games/1144/]IndieDB.

One Night 3: Full Circle in and [url=http://rpgmaker.net/games/1577/]IndieDB.

Legionwood: Tale Of The Two Swords in and [url=http://rpgmaker.net/games/792/]IndieDB.

Dude, the thread was started 17 hours ago.

For Rpg fans and unconvential setting: http://www.talesofgames.com/related_game/barkley-shut-up-jam-gaiden/ Charles Barkley: Shut up and jam.

Edit For the strategy fans the open games series.

open generals, free civ, free colonization etc. Just google for free and open.+ your favoritve classic of the past :).

The thousands of free modules for Never Winter Nights. Just buy NWN Diamonds on gog.com and play the free modules. You could play for 100eds of hours.

Stealth bastard the original.

Grand Theft Auto 1 and 2.

Have a nice doomsday

OMF 2097 is free, and there has yet to be a better beat 'em up.

Now THAT game brings back many memories... :)

[url=http://www.veloci.dk/gamebiz/gb2/ ]Gamebiz 2 [/url] is pretty cool for people who like business sims, so good that I bought gamebiz 3 a few days after, and its even better, with real names.

Yes, check out Tales of Maj-Eyal 4 if you have any interest in RPGs or roguelikes or just like a real tough challenge. It's one of the best games I've ever played and has the most interesting classes I've seen in an RPG.

Don't be put off by the simplistic graphics, before you know it you'll be completely sucked in by the stellar gameplay.

Get it here:

http://te4.org/