My favorite CD by Nancy Ajram is Ah W Noss (if you search for this album, note that it might be spelled differently because it's a translation!). Basically I love every song on that album, from the slow, sad Enta Eih, to the uptempo Taala Ya. These songs make me wanna study Arabic so that I'll be able to understand the lyrics. That is seriously a future goal of mine, studying Arabic. But that aside..
Another great CD is Ya Salam. Yay (Sehr Oyoono) is a beautiful song that you'll probably like from the first time you hear it (if you can appreciate this genre of music). I love Ashkar Aballi (please give this song a chance!), Ahla Jaw, Enta We Bass.. Well basically the entire CD as well..
I must confess I haven't really listened to her other albums as much as these two. I can't help myself, whenever I listen to Nancy I want to hear those songs I already love so I play mostly those. But I also like the song Mashi Haddi from the Betfakar Fi Eih album (again: it might be spelled differently).
Right now I'm checking out Tunisian singer Latifa, and I like what I've heard so far, but it might take me some time to actually be able to give a good review. Other artist recommendations in this genre are (Lebanese singer) Elissa and (Egyptian singer) Amr Diab. Enjoy it. And think of me when I'm in Tunisia by listening to Nancy Ajram!