It depends to your needs, you can invest your $100 to buy articles or template for your website. In my opinion firstly start to build your site/business and then you can invest where you notice that you need improvement(s).
I definatly like the idea of buying a bunch of domain names. But I would put up amazon stores on the domain names.
Start with choosing a target market first and build a squeeze page. Get a domain $12 or less, Get hosting $14 or less, and a autoresponder $1 or free 30 day trial. Traffic very cheap and start small with a $5 a day budget. Promote offers: PRICELESS. And thats how you start a 4-6 figure online business from scratch. Rinse and Repeat. Can be done with cpa or regular offers, or own product.
Firstly you have to select what type of works you can do well. If you do the design you can earn well from it.
Ratin 90, I'm a bot programmer. maybe, you'd be interested in buying some bots from me ? PM me if you want to hear what I'm currently building.
I'd say one viable option is certainly the affiliate route. Business is a long and hard process, but if you put in the effort to create a site around something you have some knowledge in and make it an authority in your niche then you could certainly make a steady income stream.
Just keep in mind that there is no "EASY" button and anything you choose to do online to make some money will be a long and dedicated journey. I find that Affiliate Promotion of "Ever Green" (never going out of style) programs such as website host companies, affiliate tools, autoresponders, etc. It's not an overnight success, it takes time and effort.
Money itself can;t make you more money unless you add Skill and knowledge to it, what you need to consider is the Time and effort which you too need to invest along with that $100 . maybe it would be good if you discover what skill do you have before you jump in with your $100 and end up losing it like many people onlien who hope to make money . if you need advice let me know .
Go to all the adverts that say make money fast with a low investment, or lots of money and no work, and after you loose your money you will have learned that there's no easy way to make money and will start focusing on real work and make some real money.
Why don't you promote products from clickbank? All you need to do is to choose products that sell well, build a landing page and use your money to drive traffic to your promotion.... BAM that's it
Just book/purchase some domains and start domain business. the lack of domain will going to make a roll in very next coming days .
Buy any one of the website from this list: http://www.b-infotech.com/social-bookmarking-websites-for-sale.php and earn money from it monthly, you don't need to spend much time on maintenance as well as content adding, users will do it for you