I've made up some new endings in my mind that would make the game even more interesting with the choices you've made troughout the game. They are probably not real ''spoilers'', but I think its better to black them out anyway :P
Ending 1: Lee has made a very good relationship with Kenny troughout the game. When the game ends with Clem walking on the countryside, Kenny managed to survive the walkers coming towards him, knowing that there's a little girl out there that needs his help. Since Lee taked very good care with Duck for him, kenny will now do the same with Clem, and they walk off together.
Ending 2: Lee has made a very good relationship with Lilly troughout the game. After Lilly is either left behind or steals the RV, she worries about Lee's and Clementine's safety, but not so much for the rest of the group. She knows that the group is heading towards Savannah, and so will Lilly. At the ending, it will be Lilly that arrives at Clementine, who will now be taking care of her.
Ending 3: Lee has not made a good relationship with both Kenny and Lilly, but he made a good relationship with Omid and Christa. The ending will be the exact same as the current ending, with both of them in the distance searching for Clementine.
Ending 4: Lee has not made a good relationship with anyone. With Kenny dead, Lilly gone and Omid & Christa lost, Clementine is now all on her own in the countryside. Knowing she lost everything, she starts crying, and the credits roll. This could be considered the ''bad'' ending, if you have been a dick all trough the game.
With all these alternate endings, it'll feel more rewarding when your siding up with characters troughout the game. In the current game, whatever choices you make, you get the same ending. That other storydriven game I like, Heavy Rain, does a lot better job with that :P. And its interesting that the choices Lee made will actually affect Clementine in the end.