The Internet is a great place to find free stuff for teens. Even if you don't have a credit card if you can take a few minutes to fill out some forms and submit them you can get tons of things such as video games, coupons, and Mp3s for free that will save you time and money.
Skin Care and Beauty Products
Teens will appreciate the free skin care and beauty products that are readily available on line. Many companies will give you free trials of their products in the hopes that you will become lifelong customers.
Cell Phones
One of the most popular and readily available things is ring tones for cell phones. Most will give you a handful of free ring tones if your purchase a subscription plan. There are also plenty of cell phone accessories and gadgets available for your phone.
Video Games
There are plenty of free online video games such as second life where you can interact in a virtual world, while sharing your adventures and making friends. Some of these include massive multiplayer online games like GodsWar and Galaxy Online. There are also classic games available for free such as Pac Man and Family Feud.
Magazines
Most teens love magazines? Because magazines make most of their money through advertising and only cover the cost of printing through subscriptions they are willing to give away a few months for free in order to get the reader hooked.
TeenFreeway 
A great site to try that is designed especially for teens is teenfreeway. This site has everything from beauty products and ideas on how to make money that caters especially to the needs of teenagers.