Nevşehir city (ürgüp, göreme. Google for "peri pacaları" you will understand..) you may find buses for a few hours of travel
Do not think about ankara the capital city, there is no point of interest.
Bodrum, Antalya, Alanya, Çeşme, Marmaris, Kuşadası, Kaş are coastal places but season may be too early when you arrive
İzmir is a nice city but it has no attractions at all (8 hours from istanbul by bus) about 5 years ago
#Turkey is my favourite country in the world. My recs are here: http://traveleater.wordpress.com/turkey-not-greece/ Cappadoccia, as Ozan recommends, is great. Also Pamukkale, a blue cruise eg from Fethiye to Olympos, and, if you can stand the crowds, Ephesus. Enjoy! about 5 years ago