Beware which time of year you travel through Turkey - we travelled in Feb and it was damned cold, we even got caught in a blizzard between Istanbul and Ankarra.
Syria - travelled through in early 99, very friendly and hospitable people. Must sees are Palmyra amazing pre and roman ruins (the Ishtar Hotel is excelllent value and very friendly people), Krak de Chevalier, and a number of other crusader castles and ancient ruins, Damascus, Madaba is a pleasant place to stop on the way south from Damascus to Jordan and the Awesome Wadi Mugib on the Kings Highway.
Jordan - agian all the people we met were friendly and hospitable, although the country was in mourning due to the death 3 days before of King Hussain. Jerash ruined roman city, Kerak crusader castle, Petra which is the most amazing city built in and from the rock faces by the Nabateans who were then colonised by the Romans, and of course Wadi Rumm - fantastic scenery and a good place if you havent tried any desert driving before. Do spend a night or two the in a cave or under the stars as its great.
Hope this helps