If your original doesn't have the river, you should get that. But most base versions of Carcassonne have the river included now. We really enjoy Inns and Cathedrals. We have Traders and Builders but seldom use it. We weren't crazy about The Count either. The princess and the dragon is a fun expansion.
As Wedin said the River, if it did not come with your version, then Inns and Cathedrals, then Traders and Builders (I like it a lot), then Abbey and Mayor. I was introduced to Carcassonne in this order (adding expansions progressively) by people who have been playing it for quite a while. They also have the princes and the dragon, but I haven't tried it as yet. Definitely recommend the other extensions, though.