Need for Speed

Hidden Jump
First pick the Rally mode of the Los Vegas track by holding down the L & R buttons, then look for the section of the track that is under construction. Go to the end of that section and then turn around and keep going untill you hit a great hidden jump.

Get the Warrior Car and Lost Vegas track
Go to the tournament and enter TSYBNS, then exit tournament mode. You now have the Warrior Car and Lost Vegas track.

Race on dirt roads
If you hold down L and R buttons when selecting a track you get the dirt road rally version of the track.

No Mercy mode: from Andrew Hernandez
Press and hold Left and Right shift buttons while "Head To Head" is highlighted. This is just like Head to head except there's no traffic or cops.

Race on Dirt Roads from Howard Falconer
While selecting your track, hold in the L and R buttons and you will get a dirt road of the selected track.