I dusted off my Gameshark disc and went through all my codes I'd saved over the years. CRT TV !
Most are still listed at the above links, but here are some I did not find listed. Some are now pointless, like the Gamespy online codes. I also can't verify all of these codes work.
Perfect Grind/Rail Balance
20423E28 00000000
No Out-Of-Bounds
207B028C 00000000
207B0278 00000000
207B0264 00000000
More Than 8 Players In A Room
00439BC8 00000000
No One Can Add You To Homie List
20434260 61720000
Can't Send/Receive Messages
204342DA 67730000
No Warps
207B0340 00000000
Debug Menu
255254D4 3FE4C9A0
Moon Gravity Online (Left-On Right-Off)
D047DC58 00008003
207AE1BC 00000001
D047DC58 00002003
207AE1BC 9C8C6DF1
Perfect Balance Online (Left-On Right-Off)
E00210003 0047DC58
207AE144 00000001
207AE194 00000001
E00240003 0047DC58
207AE144 CD09E062
207AE194 B38341C9
Press Square To Throw Combo O's
01DDFD5C 000000DD
Merge Training And School
208962B4 7078F66C
Enable Backslash Keyboard Character
21D3D684 2F000000
21D3D698 28010000
Shrek Mode (Burp Graffiti Tags, Mike V Boneless)
20423760 00000000
Burp Your Graffiti Tags
203FB708 00000000
Perfect Manual/Grind/Lip Balance, No Meters
20423E28 00000000
Another "More Create-A-Park Space" Code
003FA158 00000000
Yet Another "More Create-A-Park Space" Code
4035E534 00030001
00000000 00000000