Well, I spent most of the time in Tunis, the capital, since we had an acommodation there (cannot add tips on that one since we were lucky to get some help from a great tunisian guy who found a room for us).
I loved the city - there is a certain mixture of styles - what I consider arabic and Mediterranean (the white houses you can find in Andalucia, or the greek islands)...
The nice neighbourhoods are the rich ones El Manar and El Menzah - nice architecture, and also cafes, shops, restaurants. Cool to spend a day at.
And one more thing... the coast outside the capital is lovely too especially the beach of Hotel KARIM, so-called KARIM beach. Very nice. Getting there with a taxi costed us around 5$. Every single walk through the city!