You absolutely should see Pompeii.. go in am though as it is alot of walking and gets hot.
If your ship is docking in Sorrento then you must save time to just wander the streets of Sorrento ( the shopping is so great) and every other store offers lemonchella <sp?> tastings ( and do buy some).. also buy music boxes ( all the gorgeous Swiss style music boxes ( although Italian inlaid wood type) are all over and very reasonable as compared to US.
And take time to sit in a cafe and just enjoy that pretty town.
Sue,
Portofino you can do on your own/ and or take a city bus to Santa Margarita as in the Pinot Grigio wine.. (only about 6 bucks there too )

which is an easy few miles away..
Barcelona we have discussed in ports, but if you missed it there is a hop on hop off bus for day trippin' through the city.. you buy your ticket for one or two days of unlimited riding ( double decker English style bus) with commentary ( silly) and you can jump on and off as you wish at all the sights.. or you can hire a car-mini van with driver at about 40 EU per hour
http://www.barcelonataxi.com ( only one we use, others here may have other suggestions)
Menorca ( BUY PEARLS)..it is easy to do on your own.. but there are all kinds of hokey tours to pearl museums.. get a cab if you just like to wander
For Monte Carlo you can wander on your own all over.. if you want to venture out to surrounding vilages you can take the train ( but.. if you want to just do it easy- hire a car/ driver) my recommendation there is Jean Marc @
http://www.dream-tours.com/ have fun!