All you need is a solid idea and the passion to back it up
You can make your own website or even just a blog. Get a lot of traffic into it and then monetize it thru a number of ways : PPC, Ad placements, sponsorships, etc.
A lot of big earners on the net started out with simple ideas and put their heart into it and eventually made it big
You may try one of the following methods to market your site/blog:
Free methods:
Submission to SE's and directories
Email campaign
Forums, blogs and board postings to targetted audience
Social Bookmarking
Offline campaigns
Etc. etc.
Premium ways: (Should require a budget)
Pay-Per-Click (PPC)
Targetted Link backs
SEO
Ad spaces
Etc. Etc.
Just always keep in mind that patience is a virtue in our industry. Hope my suggestions help out.
Goodluck!
Pm me if you need more advice...