I heard placenta was good, but then when I bought it and looked at the ingredients, the one I bought had terrible, damaging ingredients in it. I used it a few times anyway, and it did NOTHING for my hair.
Over time, it would have actually caused a good bit of damage, even if I stopped using heat and colouring.
If your hair is dry, you need moisture. Try a moisturizing deep conditioner a few times a week (Aussie's Moist deep conditioner is fantastic! It always makes my hair so, so soft!) Also, look for a good leave-in conditioner.
You can also try an olive oil mask once a month (or more frequently if needed). I haven't tried this yet but plan to. I'm going to leave some olive oil in my hair maybe an hour before showering, and then wash it out.
Another thing that helped me was getting away from sulfate shampoos. I use L-Oreal EverSLEEK Repairing Shampoo. They have a few product lines that begin with Ever, and I believe they are all sulfate-free, but EverSLEEK is the only line that is sulfate and silicone-free. I didn't notice too much of a difference the first use (although I did see a slight difference), but it's been about a month and a half now, and my hair almost doesn't feel damaged at all (which is coming a long way; my hair used to be awful!)
If your hair doesn't get too oily, try shampooing and conditioning on day one, then on day two JUST condition. Sounds terrible, but if you're hair's really that dry and damaged, it actually works.
You can also try Argan Oil after a shower. DON'T use it on dry hair, but while your hair is still wet. It'll lock the moisture into your hair. I just take the smallest amount in my hand, dip my comb into it, and comb it throughout my hair, starting with the underneath (if you use too much, it will make your hair oily). You can also do a hot oil treatment with it, I've heard amazing things about it (I've for some reason never actually done it).
Good luck, I hope you find a good solution for your hair!