As with every game, Pokémon Diamond & Pokémon Pearl have their own version exclusives. However we're still in our exploration and so there may be some Pokémon outside of the Sinnoh Dex that may be exclusive to each game:

Exclusive to Diamond

Nat No. Pic Name Type 1 Type 2
#086 Seel  
#087 Dewgong
#123 Scyther
#198 Murkrow
#212 Scizor
#246 Larvitar
#247 Pupitar
#248 Tyranitar
#261 Poochyena  
#262 Mightyena  
#304 Aron
#305 Lairon
#306 Aggron
#352 Kecleon  
#408 Cranidos  
#409 Rampardos  
#430 Honchkrow
#434 Stunky
#435 Skuntank
#483 Dialga

Exclusive to Pearl

Nat No. Pic Name Type 1 Type 2
#079 Slowpoke
#080 Slowbro
#127 Pinsir  
#199 Slowking
#200 Misdreavus  
#228 Houndour
#229 Houndoom
#234 Stantler  
#363 Spheal
#364 Sealeo
#365 Walrein
#371 Bagon  
#372 Shelgon  
#373 Salamence
#410 Sheildon
#411 Bastiodon
#429 Mismagius  
#431 Glameow  
#432 Purugly  
#484 Palkia

 
All Content is ©Copyright of Serebii.net 1999-2014.
Pokémon And All Respective Names are Trademark & © of Nintendo 1996-2014