Aldi sell the small AA pocket Guides for about £1.50 Thats what we find useful & easy to carry.
Go to cruisereviews.com and you'll find loads of really useful information to help you do your own thing.
We have a guide called "Cruise guide to Europe" published by Eyewitness travel. It covers all ports in the Med, Canaries, Baltic & Norway etc. Available from WH Smith or any bookshop. Very useful.
Go on Amazon.co.uk and search for cruise guides for Med - there is a lot to choose from.
I like the DK "Cruise Guide to Europe and the Mediterranean" published by Dorling Kindersley ( ISBN 0 7513 0893 5) It's not too big to carry around , gives v. helpful advice re. ports of call and the "must sees" and even suggests which are the best excursions.
I would advise to do your own thing, the excursion prices are expensive and we did them at a fraction of the cost. example we took the train fron livorno to piza it took us an hour in all including walking to the tower it cost us approx 15 euro.. and taxi drivers are willing to take you on tours to rome, we paid £300 for 7 of us for a tour he took us to all the sights, compared to £700 NCL wanted just to drop us off and pick us up!