Lots to see and do. Don't bother taking tours - you can do it easily on your own. The tram stops opposite the port and you can get to Galata Bridge or Sultanahmet (Blue Mosque, Topkapi, and Aya Sofia) or the Grand Bazaar in a few minutes - all are on the one tram line.
Best sights are those above, plus the Basilica Cistern - opposite Aya Sofia. Also, Suleymaniye is wonderful mosque with fabulous views from the grounds - well worth a visit and free!!
Bargaining in the Grand Bazaar is good if you want gifts etc - you should pay about half what they start with, in our experience - walk away if you want to know the best price as they will follow you!
Be prepared for long lines for Aya Sofia and Topkapi.
New part of city is not exciting - stick to old city
We took a trip including Ephesus, Miletus, and Didyma - all excellent sites to visit. Great to visit in November as Ephesus was not too busy (we went in July before and it was unbearably crowded). Wonderful ruins and lots to see. In Miletus there were hardly any tourists and it has a fabulous amphitheatre.
We took a tour to the Lassithi Plateau in the mountains. Wonderful views of the mountains and coast and an interesting lokk into village life away from the tourist areas. The sail into Crete is really beautiful - we saied in at sunrise and it was magical - with the mountains spotlit by the rising sun. The port at Aghios Nikolaos is really cute - only big enough for one ship and you are right in the centre of town. All in all, highly recommended
The tour we did included a trip to a monastery with great views over Rhodes countryside and coast - well worth doing. The a tour of Rhodes old town, including the Grand Master Palace. Great mosaics in many rooms and interesting history to listen to. Rhodes town you can do on your own - no need to do a tour, just walk around - it is quite small and the city walls make it clear where the town begins and ends. Port is close to the city and you get great views sailing in and out, and from the docked ship if no other boats in the way!!
It is a long drive but Delphi is wonderful - great ruins in the most magical spectacular mountain setting. Our guide was useless - she talked incessantly and would not have allowed enough time to see it all if we hadn't left her and explored the site on our own. It is quite a hike up to the top but worth it for sensational views. The museum is also very good - not too big but great displays and well exhibited