If you go to your minecraft saves folder (usually something like C:\Users\%username%\AppData\Roaming.minecraft\saves) there will be a folder called players.
Go into that folder and delete the file with your name on it, and the next time you enter the world it should spawn you close to 0,64,0 rather than the extreme location you teleported to. Note that you will lose any items and experience you currently carry.
An alternative solution is to use a third party program like MCedit to edit your .dat file and change the location in the file. I'm afraid I don't know much about those though.