Ill list a few - some of which people already listed, but here we go anyway:
Domain Parking - Though arbitrage isint allowed anymore, people are still making money from this.
CPA (COST PER ACTION): If you can figure out the right niche and or the right product to use, you can end up making thousands of dollars per month from this.
Blogging: You can either blog FOR people and make money doing this OR you can make money yourself by using something like Adsense or another program like it.
Service Provider: You can make money offering ALL kinds of services to people. Everything from Web Development to Writing content for people and everything else in between. This is probably one of the easier and more profitable options.
PTR/GPT: I don't really LOVE this option, but some people really get into it. The Paid To Read and Get Paid To industry has been around for a LONG time. Its all about clicking ads in emails and clicking ads, banners, links on specific websites. It wont make you millions and it depends a lot of how many referrers you get, but you can make money nonetheless.
Affiliate Marketing: This is going to allow you to sell services and products for OTHER people. You will get a percentage of whatever the sale is. Sites you can check out are Clickbank, AffiliateJunction, Linkshare, etc. These are what I like to call "hubs" they are programs where you can find hundreds if not thousands of different Businesses and Companies to sell their products.
You can also find tons of individual Affiliate sites as well. Nowadays, almost every site online has a "Become An Affiliate Option" on their website! They are all going to offer different options, so shop around and see which ones you like the best. Advertise their products and services through things like PPC (which costs money) or you could do it for free with things like Blogging or Article Marketing.
Paid Surfing/Filling Out Surveys: This is an old "been there done that" option for me. Its almost like PTR/GPT where you are getting paid to surf (usually a very small percentage) or you are getting paid to fill out surveys. Money is money though!
PPI/PPV/PPC: PayPerInstall, PayPerView (not on your TV) and PayPerClick (not the kind you use to advertise YOUR site) can BE good ways to make money. But like CPA you really need to find the BEST way to make said money and this can sometimes be difficult. PPV is nice because if you have enough traffic coming to your site and you have something like a Video that plays every time the page loads for a new unique IP - you get paid. But you also have to have a ton of visitors to even make anything worthwhile!
Freelancer: For me, a freelancer and a provider are two different things, but I guess for some people they are the same thing lol. As a freelancer you can take something you love to do or are good at - and make money from it. Everything from writing ebooks to Photography. You can also sell your stock photos on Stock Photo websites as well. Pick your poison!
Selling Domain Names: Check THIS site out lol. Enough said.
Flip and Sell websites: This is going to take MONEY to do and from what I understand you dont really want to spend money, you want to make it. Either way developing and website flipping can become a very profitable option. Its not all about appearances though. Just because you have a $5,000 web design doesn't mean its going to sell for a ton of money. You also need to make the page rank, SEO, SEM, SERPs, visitors, etc happen as well! I think this is a lot of work, but as said above it CAN pay off!
Work At Home Jobs: There are about a BILLION people/companies/businesses online looking for people like you that want to do admin jobs, MLM, Networking, etc. You gotta watch out for the scams on this though -- majorly! You can also check out Craigslist for this as well. But watch for people that don't say too much of anything and yet they want you to contact them NOW. Look for gigs, VAs (virtual assistants) and Marketers. I just hired a Marketer and I pay him a pretty good salary for getting me customers
Sell Stuff on eBay, Craigslist or Amazon: If you can either find "treasures" in your area or you can find some really great sites online that AREN'T saturated and have LOW prices - you can actually start selling stuff on these three sites. Frankly, they all have their different benefits. I like ebay and Amazon because its sites people are ALWAYS on. But I also like Craigslist because there are NO fees involved whatsoever, and if you sell locally, you can even save on shipping and handling as well.
Okay. I over-typed. Sorry!