Verified answer

http://www.serebii.net/black2white2/exclusives.sht... different pokemon

http://www.serebii.net/black2white2/versionarea.sh... different areas

http://www.serebii.net/black2white2/versionmisc.sh... Miscellaneous

The main differences are whether you get Reshiram or Zekrom, and in Black and White, whether you fight Drayden or Iris as Opelucid City's Gym leader.

Some areas are different between versions, like Opelucid City, as well as the garden at the end of the Mistralton Airport's runway. In Black 2 and White 2 Route 4 (the one north of Castelia) is different as well.

Pokemon that appear differ, but that goes without saying. Though in Black 2 and White 2, there's some pokemon that appear on certain weekdays.

You'll find a Jellicent with its Dream World ability in Undella bay, its gender depends on what version you are playing. In white 2, you can find an underleveled Braviary with its Dream World ability on route 4. In Black 2, you find a Mandibuzz with its dream world ability instead. These pokemon only appear on certain weekdays.

In Black and White, trainers will tend more toward triple battles (white) or rotation battles (black) and you hardly see the other style. The Battle House in Opelucid also reflects this.

In Black and Black 2, you will have access to a city called Black City to the south of Undella town. In White and White 2, White Forest will be there instead. In Black 2 and White 2, Black City will have the Black Tower, while White Forest will have the White Treehollow. Completing areas in these places will cause up to four shops to open. Depending on the version, different items are available for sale. The reward for clearing all 10 areas is different as well. In Black 2, you get a Shiny Gible, in White 2, you get a Shiny Dratini.

I'm sure there's other things that I missed, but there's quite a list of differences. But some of them are not as easily noticed as others.