Another great way to leverage the product review is to ask for two or more additional items for a giveaway.
Techically, according to legal terminology you are holding a sweepstakes because the winner is chosen by random selection. But since no one uses that word, I'll call it a giveaway.
A Giveaway is Good for You
Yes, a giveaway is a bit more work. But the upside is that your readers are excited about the possibility of getting something for free. You want your readers to be excited about your blog posts and not roll their eyes, clicking away with a sigh, "Another product review! Ugh!"
Instead you want them to think, "Oh, goodie! I might win!" They are also more likely to tweet and share your post which means more traffic for you.
A Giveaway is Good for the Company
When your readers are engaged, there more eyes to see the product you are reviewing. When there is social media buzz surrounding a giveaway, companies receive more branding recognition and reputation.
If you use Wordpress (and you should), get the And the Winner Is WP Plugin for managing contests. It's a dream!
When you send your product review proposal to the company and ask for extra product to giveaway, ask the company to ship it directly to the winners. This saves you hassle and cost of postage.
State your rules clearly. I usually add a disclaimer that it is only for ages 18 above and for residents of the continental USA. (This leaves out your international readers, so when at all possible, have an ebook version or offer to pay the postage for them if they should win. I was an "international" once; it stinks to always be left out of the fun.)
In the giveaway post, tell exactly when you will choose the winners and that they will have X number of hours to respond or another winner will be chosen. This saves you from waiting days and days for a winner who never sends an address.