An excellent source for internet printable (or IP) coupons is Coupons.com. In fact many times when you request to print a coupon from a product/manufacturers web-site you will use Coupons.com's program Bricks. They have a large selection of coupons to print and regularly get new offers. There is a limit to how many you may print so make sure you plan on using them before their expiration date. Most couponers agree you should wait to print till you're ready to use them so they don't expire on you.
All you have to do is scroll through their offers clicking on the check boxes next to the ones you'd like. Then, click on the print button. You will be prompted to download their printing program if you've never used it before. Then, if you're printers on, out will pop your coupons and you'll be off to the store and saving.