While planning my first cruise, i did quite an extensive research on various ports of call in the caribbean. I am therefore going to try and give you as much help as i can on your ports of call, so you donot have to go through the rigors that i went through. Here goes.
Curacao
[www.curacao.com] . this site gives alot of great info on the various activities to be found.
Isla Margarita
[www.islamargarita.com]
Barbados
[www.barbados.org]
Dominica
[www.dominica.dm]
Here are some email addresses of local tour operators in Dominica.
tavernier_d@hotmail.com - Reyno Tours

benox265@hotmail.com - Beno Tours

fredos40@hotmail.com - Fredo Tours

While i can only vouch for Fredo Tours,( you can read my review on Cruise addict -
http://www.cruise-addicts.com/explorations/readreview.php?id=0000000007) the others have also been used and gotten good reviews. Though some people had some really rotten experiences with reyno tours. I remembered on our cruise, one couple had to pay US$30 pp after reyno had already confirmed their tour at US$25 pp, since he did take them on the tour himself as planned. What he does is get the tours and distribute them out to other taxi drivers. In my opinion he is a "pimp" : nono:.
From reading some other reviews, Beno is very good.
St. Thomas
[www.usvi.net]
Princess Cays
[www.cruiseweb.com]
Happy cruising.