Eevee has the most Evolutions(7 to be exact and maybe more in Black and White coming out:)), if thats what you mean. If not, Darthdestiny is right, no pokemon can evolve more than twice.
Pokémon may evolve up to 2 times, eg. starters, baby+basic+new evolutions, etc
None,but maybe in Black and White there might be pokemon that might evolve more than 2 times.