Pokemon black and White are DSi Enhanced. As far as I know, the only features added are video chat and the ability to keep track of the battery life of the DSi while playing a game.
Furthermore, Sonic Classic collection (the four in one game) is DSi enhanced. It takes advantage of the extra horsepower of the DSi (twice the CPU and four times the RAM) to make the emulation better than on a normal DS.
Certain puzzle games (like Ubisoft crossword games) might allow you to save more puzzles to the SD card of the DSi, although I'm not sure if this is actually the case. It probably is though, because I've seen signs on the box saying "Has extra features when used in a DSi" or something like that.
And that's all I really know. Hope I...