The current method I'm using is through financial solutions.
I'm currently designing a website to facilitate all of the different systems I use now - but the idea is essentially the same as Nomi's. Find something that you enjoy doing - and are actually interested in. From there - build it, and they will come.
If you want to see a turn key system that's currently working - only used for an example:
http://fxtrainer.com [main website]
http://eflormata.fxtrainer.biz [turn key mirror version] <-- yes, this is mine.
This is the site I'm basing my own on. It's going to be more than just Foreign Exchange however - as it will go into Tax Planning, RRSP solutions, Investing Systems, etc. Just pick an honest topic that you're willing to put a lot of time into - and go for it.
On a side note.. if anyone can recommend any decent webhosts on Microsoft servers (for .NET applications) please throw them my way. I also run a software consulting company on the side and am looking for hosts to recommend to my customers. PM me please in respect of this thread.