I don't know about you, but I'm a big fan of getting things for free. Even if it's something you wouldn't have normally purchased, getting a free gift in the mail just brightens your day. Many shops and businesses use giveaways as a promotion tool. They offer up an item as a prize for the giveaway and, ideally, more people look at their blog, website, or shop as one of the conditions of the contest.
Each giveaway has certain conditions for entering. The main/mandatory entry usually involves visiting the shop, blog, or website of the person/business giving the free item. Some sites allow extra contest entries for following their blog or Facebook page; blogging, Facebooking, or Tweeting about the giveaway; making a purchase; etc. How much you do is up to you. My participation usually depends on the site and the giveaway item. Sometimes I find some great new blogs or places to shop from.
Some of the sites host their own giveaways, while others list giveaways being hosted on other sites. Here are some of the giveaway sites I've found:
Giveaways on the Web
By Hand Giveaways
I've won a few giveaways already and it's so much fun!