If you want to power level quickly I reccomend the following two guides: for instance  Brian Kopp's 1-70 power leveling guide  And for Horde power leveling the famous Johana and Macow 1 to 70 Horde guide
     For free tips read on, plus get your free guide at the bottom.
     If you are an alliance player Brian Kopp's famous 1-60 guide which is now even more famous because it is, following the Burning Crusade expansion, now better known as the 1-70 Alliance Wow power leveling Alliance guide. This guide does exactly what it says on the pixel tin that it has been packaged in.
Johana's 1 to 70 Horde guide or to be more exact Johana and Mancow's (the two characters who are the main protagonist in the guide) is the definitive guide for Horde players who want to power level from 1 to to 70 because, don't forget, the Burning Crusade has added a further 10 levels to the game with future releases and add ons which will no doubt increase the number of levels even more.
Now if you can do better than this, then please send me the guide and I will pay you handsomely for it .