Dave
I am a member of the Bob Clubs,
http://www.bobclubs.com/ unlike the BNI where you have to give out refferals at every meeting, the Bob clubs would rather you only gve out solid refferals, not just names and numbers on companies who are not nessasary looking for your services.
I have found them very useful, I have picked up more regular and one off work, that has covered all the fees I have paid out, with all the regular work I have gained, it is more than enough to cover all my fees for years to come.
Apart from the extra business it can gain you, there is also the benefits of meeting other business people who can help your company move forward.
You need to be precise on what you are looking for, instead of saying that you are looking for window cleaning work, narrow it down to what work you are looking for, even what companies you want to be introduced too.