Using a heat protectant when flat ironing your hair is oh-so-important. There are quite a few good brands out there, including Ion, which you can often find in your local beauty supply store. You can't beat the price of a product this good; it performs like one you'd find in a salon, but for much less.
What It Does
It protects your hair from heat styling tools with a combination of moisturizing jojoba and anti-frizz elements. I happened upon a tube of Ion Healing Jojoba Flat Iron Cream at my local Sally Beauty Supply and decided to try it out.
How to Use It

After flat ironing
Photo © 2010 D. Sandeen, licensed to About.com, Inc.Apply the cream to towel-dried hair and comb through. The beads are only activated with heat, so there's no point in using this cream if you're not going to use a curling or flat iron. After applying to damp hair, I air-dried until the hair was about 75% dry and then followed with low heat, working through with a vent brush.
Final Verdict
I love this product, and not just because I think it's a bargain. All I used on the hair in these photos was the cream -- nothing else. Once the heat is applied, the hair smoothed out beautifully, and wasn't greasy or weighed down. I worked in small sections of about one-inch and with each pass, the hair transformed into silky, lightweight lengths. Even though it was a little humid when I used it, the hair didn't revert. It remained incredibly soft and light throughout the week.
Salon brands are often worth the money, but this is one less-expensive alternative that works great. If you routinely heat style your hair and need a heat protectant, I strongly recommend this one from Ion.