Having pegs on your bike when riding flatland helps. Chad Johnston has shown you can ride without pegs but 99% of the riders out there use some sort of axle extenders. Here are some from St. Martin:
-7075-T6 alloy
-38 mm O.D
-112 mm long
-grip or knurling
-surface re-designed end, rounder
-Weight : 8.4 oz
-Color : black - dark red - shinny green