There are a few threads about this I believe. Here is my idea, if come tomorrow you were forced to choose a different career what would you do? Got it? Now spend that extra time learning everything about your choice if you chose something that you could manage along side this career, great, do it. Unfortunately as little as we make as airline pilots if we were forced out of the industry tomorrow most of us would have to take a pay cut because our skill isn't greatly appreciated elsewhere.
Web programing is an easy to do on the road, it's however a very competitive industry.
Real Estate if you have some cash saved up there are still some killer deals out there right now for potential FLIPS and rental property to eventually sell when it becomes a sellers market again. I don't recommend taking out a loan to buy new property even though the interest rates are record low, it is a risk I personally cant afford to take.
Lawn Maintenance: if you are home at least 2 days a week this is a great way to stay in shape and make some good money. I used to do this it is a ton of work, but I averaged $600-$800 a day... It got to big for me I had to hire people just to get to all my clients, working sun up to sun down on my days off was tough too.
On a side note I'm a big Dave Ramsey fan, and believe the best way to make money is to stay out of debt so don't borrow money.