Drop shipping eCommerces sites. I've been doing this for 5+ years full-time. Starting out - like anything - you need to do a lot of the legwork yourself but now I only spend a few hours a week managing my team and it provides a healthy full time income. And with drop shipping, all the fulfillment, purchasing and warehousing is handled by someone else.

I know drop shipping can get a bad reputation, but when done correctly it can be an effective way to create a passive income streams. If you can program well, I'm not sure if I'd recommend it over a SAAS based approach. You'll likely be able to make more money with SAAS as you're creating your own products vs. selling an existing one. But the long-term upkeep is generally less for eCommerce vs. SAAS (guessing here, as I've never run a SAAS business).

Margins are a bit lower with DS, so it does take a while to build some organic traffic and marketing buzz. But once that starts to gain some traction, it's not too much work to get a team in place and automate things. And if you're willing to put in the time to make a high-quality site that addresses customer questions and buying hesitations up-front before the sale, it's even easier to automate on the back end for support.

But you do have to be careful about niche selection. Because drop shipping markets are fairly competitive (low barriers to entry), you have to be really selective about what nniches you get into. Specifically, I like to see really confusing niches where I can add lots of informational value, plus lots of accessories I can sell to increase overall margins). For anyone who is interested, I wrote a blog post on the three crucial things I look for when picking a niche for eCommerce and drop shipping:

http://www.ecommercefuel.com/anatomy-of-profitable-niche/