1st Row - Female character on top of some sort of mansion or castle; Male character in a room (which kind of looks like a Union Room); Floaroma Town's new look. And since the storyline of Platinum involves Shaymin, it makes sense that they would add more features to the town.

2nd Row - New characters? Only the Japanese game designers would know who they are; the Torn World, which takes advantage of both the DS screens (this dimension warp is above the Spear Pillar); Shaymin's Sky Forme in battle. Evidently, if a Shaymin was to be traded over to Platinum, it would then transform into the Sky Forme. Trade it back to Diamond/Pearl, and it'll revert back to its Land Forme.

3rd Row - Regigigas VS Regirock; Male character in Regice's chamber, and in Registeel's chamber. This heavily hints that the Regi Trio is obtainable in Platinum.

Look at the cool badges! ^^

My sprite-scratched Sky Forme Shaymin.

The CoroCoro scans of Shaymin (Sky Forme) | the 4 Regis | the Trainers' new oufits.

The Pokémon Platinum cover design.

Male Trainer with his new clothes, in a battle with the Origin form of Giratina.

The Team Galactic Leader, Cyrus, standing before Giratina.

Giratina's Origin Form