Saving / Investing for my kids college tuition - What's the best approach?

I'm trying to figure out the best plan to save and invest $ for my kids college tuition. I live in Texas, and they have a few different savings plans that basically lock in the price of tuition today for any public college in the state. I can do monthly installments for this, however there's a 8% annual interest charge. If my kids want to go out of state, I believe I can get all my $ back, but I don't think I get any interest on it.

So is it a good idea to buy into these plans, or rather invest in something else that I'll get a return on? Tuition prices have gone up a ton the past few decades and maybe locking in the tuition price today is a good idea. I really just don't know...

Anybody care to share their opinion on this?