LPT: If you are given a prepaid debit card as a gift, save it after you spend the money. You can use it to sign up for free trials online without worry of being scammed.

Alternately, get a Bank of America or CitiBank MasterCard which let you create custom credit card numbers for use with a single merchant, with a credit limit and expiration date set by you. Once a merchant uses the card one time, the number cannot be used by any other merchant. You can go back later to extend the credit limit and expiration date.
They're controlled payment numbers. BoA called it ShopSafe. Citibank calls it Virtual Numbers.
Create a card with a $1 limit that expires in 2 months. You're set for all free trials.
Unlike a regular credit card, where retailers can continue charging your account when your card expires, I've never had a retailer successfully charge me after having used a temporary card number.