Gary

Crystal Dragon:

Ash's long life rival, Gary Oak. What fun would the show be if Ash didn't have a rival?
In the game, Gary used to be your friend, but then became your rival, though in the show, he's always been the rival. Gary is very arrogant and thinks he's the best with that fan club and cheerleaders.
He is the grandson of Professor Oak. He is always a step ahead of Ash, and makes fun of him every chance he gets, making Ash feel bad for being so far behind (until Misty stands up for him ^-^).
Gary has no nickname, but his Japanese name is Shigeru.

Here is Gary's line up of Pokemon:

Bulbasaur/Ivysaur/Venusaur (uncomfirmed)
Krabby
Nidoran(female)/Nidorina/Nidoqueen
Arcinine
Others are unknown

Gary Links:
Ego And Soul
Arrogance: A shrine to Gary Oak
 

June:

You notice in the beginning of the TV and comic book that the two are obviously rivals. It seems like in the show Gary automatically considers himself Ash's enemy. However, you soon learn that it's just Gary's odd way of showing his friendship to Ash. 
Also, you may notice that Gary's arrogance is only directed towards Ash, making the two very good friends indeed. =) 
He seems like a popular guy, especially to have a squad of voluntary cheerleaders follow him around. Heck, they cry when he losses and even chant cliché mottos to boost his ego.