There've been quite some threads asking for these and so here are some links.
One Piece Games
–------------------------------------------------------------------
GBA ROMS/PS/PS2 ISO etc.: irc.rizon.net #kaizoku-fansubs K-F|Smoker Files list @ http://animemedia.org/smoker.txt
Other Games
–------------------------------------------------------------------
www.dgemu.com (Registration Required) - Loads of ROMS including GBA, GBC, SNES, N64 etc.
www.emulator-zone.com - Find the emulators you will need there.
thepiratebay.org - Not a ROM site but hop over there to look for torrents to your PS/PS2 ISO.
http://solops2.com/torrents.php# (Registration Required) - PS2 .ISO
http://www.blackcats-games.com/ - Registration required.
www.mininova.org - Not a ROM site but hop over there to look for torrents to your PS/PS2 ISO.
http://nds-roms.com/ - Nintendo DS Roms
Emulators
–-------------------------------------------------
www.emulator-zone.com
Reply here for more links or to request for specific games.