A lot of my friends have Jellicent. I want to catch one too.
For Black/White 2
Route 4, Route 13, Route 17, Route 18, P2 Laboratory, Undella Bay, Undella Town, Virbank City, Virbank Complex, Humilau City, Seaside Cave, Route 21
Black/White 1
Route 4, 17, 18, Driftveil City, P2 Laboratory
Source
In Black/White: Routes 4, 17, 18, Driftveil City, P2 Laboratory
In Black/White 2: Routes 4, 13, 17, 18 and 21, Virbank City, Virbank Complex, Undella Town, Seaside Cave, Humilau City, P2 Laboratory, Undella Bay
http://bulbapedia.bulbagarden.net/wiki/Jellicent#Game_locations