TTR is fantastic, if you are likely to play with 3 or less players, get Nordic Countries.
As for Carcassonne expansions, I recommend the following:
Inns and Cathedrals (we ALWAYS play with the rules of this one),
The Princess and the Dragon and
The Tower
The latter two are definitely better with more players and not really recommended with 2. But we play with the tiles from the majority of the expansions and just switch in and out the rules we want to play with. Setting a time limit of the game, otherwise it can go for a long time
Edit: And if you don't have it, get this mini expansion:
The River II