Here are my free TTP maps of Istanbul, and here's a free Google map. Farther down on this page are many more, detailed paper maps of Turkey available from Tulumba.
Istanbul Region Map (free TTP map)
Showing Bandırma, Bursa, İznik, Yalova and the Sea of Marmara.
Google Istanbul Map
This is the basic Google map of the city. Don't trust placement of landmarks or even places of business. Some are correct, but many are woefully erroneous.
Istanbul's Top Sights Map
Shows Old Istanbul's top historical and cultural sights, from Topkapı Palace to the Grand Bazaar.
Topkapı Palace Map
Shows the location of this prime Istanbul landmark, and also Gülhane Park, the Archeological Museums, Tiled Kiosk (Çinili Köşk) Ayasofya (Hagia Sophia) and the excellent Sirkeci Konak Hotel.
Basilica Cistern Map
Shows the location of the Basilica Cistern (Yerebatan Saray Sarnıçı) between the Hippodrome and Hagia Sophia.
Divan Yolu Map
Details of the old Roman/Byzantine road from Sultanahmet westward past Çemberlitaş and the Grand Bazaar toward Rome.
Bosphorus Cruise Map
All about taking a cruise on the Bosphorus toward the Black Sea.
Atatürk Airport Map
Map locating Istanbul's prime international airport in relation to the city center and major sights.
Little Hagia Sophia Map
The neighborhood of Küçük Ayasofya, not far from the Sultanahmet (Blue) Mosque and the Hippodrome, has many hotels, restaurants and shops as well as the Little Hagia Sophia Mosque (Küçük Ayzsofya Camii), formerly the Church of Saints Sergius and Bacchus.
Lonely Planet Istanbul Map
You can get your own copy to take with you.
Istanbul Satellite Image
The main parts of the city are labeled on this high-altitude image on the main Istanbul page.
Istanbul from Space (Poster - from Tulumba)
Istanbul Metro & Tramway Map (free TTP map)
Shows how to go between Atatürk Airport, the Otogar(bus terminal) and Sultanahmet Square quickly and cheaply.
Istanbul Asian Shore Street Plan (from Tulumba)
Istanbul European Shore Street Plan (from Tulumba)
Istanbul Bosphorus Map (from Tulumba)
Istanbul Pera-Nişantaşı-Kumkapı-Ortaköy-Kadıköy-Yeşilköy Urban Residential Plan (from Tulumba)
Istanbul Peninsula Historical Map (from Tulumba)
Istanbul Map of 1715 (from Tulumba)
Istanbul Map - Cartoon Style (from Tulumba)
Istanbul Street by Street (from Tulumba)
Bakırköy (Istanbul) Street Plan (from Tulumba)
Beşiktaş (Istanbul) Street Plan (from Tulumba)
Beyoğlu (Istanbul) Street Plan (from Tulumba)
Bosphorus (Istanbul) Map of 1764 (from Tulumba)
Bosphorus Satellite Image (free TTP map)
The main Bosphorus page has a high-altitude image showing the strait that connects the Black Sea with the Sea of Marmara right through the heart of Istanbul.
Kadıköy (Istanbul) Street Plan (from Tulumba)
Ortaköy-Kadıköy-Yeşilköy (Istanbul) City Residential Plan & Map (from Tulumba)
Şile City Plan & Map (from Tulumba)
Şişli (Istanbul) Street Plan (from Tulumba)
Sultanahmet Street Maps (free TTP map)
Small maps showing the location of principal hotel streets in Old Istanbul (Sultanahmet Square).
Üsküdar (Istanbul) Street Plan (from Tulumba)