In the Pokémon Global Link website, there will be a poll from September 18th, 2010 to Novmber 1st, 2010 in which a Pokémon should be chosen. The winner of the 1st place will be accessible in the Dream World starting from November 5th, 2010 till January 31st, 2011. Although the website didn't specifically name any of these Pokémon that will be in the poll, but there were several Pokémon that appeared within the image:
Bulbasaur, Charmander, Squirtle, Mewtwo, Mew, Chickorita, Cyndaquil, Totodile, Lugia, Ho-Oh, Celebi, Treecko, Torchic, Mudkip, Groudon, Kyogre, Rayquaza, Jirachi, Deoxys, Turtwig, Chimchar, Piplup, Dialga, Palkia, Giratina, Manaphy, Darkrai and Arceus.
These are probably the Pokémon that people should choose from.

Source: Serebii

If those Pokémon will be become accessible in the Dream World, does that mean they'll have alternative abilities? Or is that not necessary?

Anyways, I hope we get such polls when the American Black & White come out because they seem to be interesting.

If we can choose Celebi, I'm going to vote for him. The lack of a legit European Celebi disappoints me (Even though this one would be Japanese )

Whether or not I'll be able to use the Dream World, though... I dunno.