Most of the Pokemon mentioned under the Dream World list assume that you catch the base stage and then evolve it -- for example, you can't find Exeggutor in the Dream World, only Exeggcute.
Available normally
Swoobat
Musharna (postgame only)
Espeon
Sigilyph
Gothitelle (Black 2 only)
Reuniclus (White 2 only)
Claydol
Beheeyem
Grumpig
Lunatone
Solrock
Starmie
Bronzong
Metagross
Available through Dream World
Pleasant Forest
Exeggutor
Girafarig
Xatu
Windswept Sky
Sigilyph
Sparkling Sea
N/A
Spooky Manor
Hypno
Mr. Mime
Grumpig
Chimecho
Beheeyem
Alakazam
Reuniclus
Rugged Mountain
N/A
Icy Cave
Lunatone
Solrock
Claydol
Dream Park
N/A
Available via Dream Radar
Musharna
Sigilyph
Starmie
Gardevoir
Gallade
Bronzong
Jynx
Metagross
Slowbro
Slowking
Available via DNS exploit
Mewtwo
Metagross
Deoxys
Meloetta
Victini is also available through DNS exploit, but only in Black and White. In addition, several Dream World Pokemon, like Slowbro and Wobbuffet, are only available in Black and White's Dream World.
It's not particularly practical to use any Pokemon not found in the base game. You can reasonably get through a Monotype playthrough without using the Dream World or Dream Radar, and they might only serve to slow you down.