Linking to illegal derivative works probably violates the rules of that forum but fortunately linking isn't a crime. The below links may be patches and not the ROM itself. The ROM itself can be found on your local torrent site, probably in a pack that includes every SNES or NES ROM!

Brutal Mario: http://www.smwcentral.net/?p=showhack&id=1012

Extra Mario Bros: http://www.derok.net/nes-roms/super-mario-bros/extra

Sonic 2 Long Edition: http://forums.sonicretro.org/index.php?showtopic=11648&s... (try PMing people in this thread or going on their IRC channel)

Zelda Parallel Worlds: http://zeldaparallelworlds.googlepages.com/

The Second Reality Project: http://www.romhacking.net/hacks/41/

Sonic Megamix 3.5 (4.0 isn't out yet): http://info.sonicretro.org/images/3/3f/S1MMU.rar

Super Metroid Redesign: http://drewseph.zophar.net/

Mario Adventure: http://www.vintagecomputing.com/index.php/archives/63