The differences in each game are very small. Significant ones are as follows: 1. White/Zekrom and Black/Reshiram. As with every Pokemon game; each version has different legendaries available in them. Pokemon White gets Zekrom, who is Dragon- and Electric-Type. Pokemon Black gets Reshiram, the Dragon and Water-Type.
Other than that, there are minor differences such as in White you get the White Forest, and in Black you get the Black City. Also, certain battles in each game will be different in the type it is. In Pokemon Black you could have a double battle whereas in Pokemon White you could have a triple battle. There are certain pokemon in each version that are exclusive, but that is easily rectified with the WiFi trading system (check here
for the trading forum).
That's all there is to it, really.