Brad and Jamis have given you good advice.
Rental houses have been very good to me.
You benefit from 1) appreciation; 2) mortgage paydown; (by your tenants!) and 3) tax write offs, especially depreciation.
You do need to read some books and take some seminars on investing in rental houses. Avoid the guys who make their money from selling courses. Look for seminar teachers who actually own lots of real estate themselves. The first kind can only lead you astray, and that can be extremely costly. Some of the best courses are by Jack Miller and Jimmy Napier. Avoid the get-rich-quick and the no-money-down guys. Just buy good houses, at least a bit under market and in decent neighborhoods.
And you must learn ways to buy houses under market. In some markets where prices are still comparatively low, you still have plenty of upside. In overpriced areas, your risk is multiplied many times and you may get wiped out. These houses, too in time will probably go up. But you can lose your shirt while you wait.
And as mentioned, you need cash reserves to tide you over vacancies and repairs.
It's like any other business or investment. You've got to learn how to do it.
But it's very safe once you learn a bit and since real estate in decent areas trends up, this form of investment is more forgiving than most others.
When you own rental houses, time is truly your friend.
matis