Here is every Pokemon with the potential for 5 stars in the skill stat:
Ivysaur, Wartortle, Raichu, Sandshrew, Sandslash, Clefairy, Clefable, Ninetales, Persian, Psyduck, Mankey, Abra, Kadabra, Alakazam, Tentacool, Slowpoke, Slowbro, Muk, Haunter, Gengar, Hypno, Hitmonchan, Mr.Mime, Scyther, Jynx, Magmar, Ditto, Vaporeon, Jolteon, Articuno, Zapdos, Moltres, Mewtwo, Mew, Bayleef, Meganium, Hoothoot, Ledyba, Ledian, Chinchou, Pichu, Bellossom, Sunkern, Espeon, Slowking, Unown ! and ?, Wobbuffet, Scizor, Sneasel, Remoraid, Smeargle, Hitmontop, Suicune, Ho-oh, Celebi, Treecko, Grovyle, Sceptile, Blaziken, Marshtomp, Zigzagoon, Wurmple, Dustox, Lombre, Ludicolo, Ralts, Kirlia, Gardevoir, Breloom, Meditite, Medicham, Roselia, Grumpig, Vibrava, Cacturne, Seviper, Baltoy, Claydol, Anorith, Milotic, Kecleon, Regirock, Regice, Registeel, Latias, Latios, Kyogre, Groudon, Jirachi, Deoxys Attack Defense and Speed forme, Monferno, Infernape, Kricketune, Roserade, Burmy-Plant Cloak, Vespiquen, Pachirisu, Floatzel, Cherrim, Ambipom, Mismagius, Mime Jr., Garchomp, Riolu, Lucario, Skorupi, Drapion, Croagunk Toxicroak, Abomasnow, Weavile, Magnezone, Lickilicky, Tangrowth, Electivire, Magmortar, Glaceon, Gliscor, Porygon-Z, Gallade, Froslass, Regular Rotom and Frost and Mow Rotom, Azelf, Dialga, Palkia, Heatran, Regigigas, Giratina Origin Forme, Cresselia, Phione, Manaphy, Darkrai, and finally every Arceus forme.
Keep in mind that the nature of the Pokemon also affects their Pokeathlon stats.
Sources:
http://www.serebii.net/heartgoldsoulsilver/pokeathlon-pkmn.shtml
http://bulbapedia.bulbagarden.net/wiki/Performance