10 to 15th way

10. Domain parking and type-in traffic: People sometimesThe witch has spoken guess at URLs. If they want a plumber they may try plumber.com though they've never used that site themselves. Find terms that people may be typing in (I will provide a detailed guide to this when I get a chance), buy the domain and populate it with ads. There are several ad programs to monetise your parked domains. Or combine this with the previous idea to buy plummer.com or similar typo domains to make money online.

11. Drop catches. People sometimes forget to renew their domains and these expire. Picking them up will give you some remnant traffic from sites that link to this domain/people who've bookmarked it etc. In some cases the traffic can be pretty high. Provided you're fast enough to replace the copyrighted content that was there with something else you can make quite a profitable business from doing nothing else but this.

12. A variation on the above. Sell the domain back to the previous owners. Note that you may want to tread carefully and get familiar with the rules for that TLD before you start sending off ransom notes. For example, with ICANN (domains that end in .com, for example) the moment you send the previous owners an email saying you've got their domain and you'll give it back for $10K... you've lost. It can't look like a ransom demand. Be reasonable and read the small print of the UDRP. No UDRP required if you're sitting hostage on myspace.com/theircompanyname or the equivalent at blogger, twitter or other big destination. LOL, watch them kick themselves and sack their web advisors who told them about taking the "dot info" but omitted to mention the importance of protecting the brand by owning the associated myspace directory (and others)! And it costs you nothing!

13. Run a domain management service. Hundreds of thousands of webmasters (or more) have a large portfolio of domains. A lot of them would like the boring bit taken out of their domain management. You can run their DNSes or just a service reminding them when each domain comes up for renewal. Or an automated monitoring service to tell them when one of their domains/sites is inaccessible.

14. Start a directory to list domains for sale. That's what people like SEDO do. You can get money just for allowing domains to be listed in your directory.

15. If you're running a service putting buyers and sellers of domains/sites in touch with one another you could get money for add on services (like providing escrow facilities). For ideas have a look at what existing domain intermediaries offer.