I have several domain names producing 2000 page impressions per day of
unsolicited generic traffic.  I currently show Google ads courtesy of
Sedo who consolidate many users' websites.

I use the keyword casino, and a reaonable number of people click on an
advert each day, but I only get $0.30 or so from each click because
the bidding for the keyword casino on Google is at quite a low level. 
It looks like this is that case because Google don't show adverts from
actual online casinos, just from associated services.

Meanwhile, Overture (Yahoo Search Marketing) does allow casinos to
advertise, and the bidding on the keyword casino is $5.00+

So I would prefer to show Overture results.  The problem is Overture
only deals with websites providing more than 500,000 hits per month
and I don't fall into that category.

So the question is what companies are out there who consolidate
websites and show Overture adverts on them (in the same way Sedo does
with Google ads).  And what commissions are these companies taking
from the advertising revenue they produce, so I can make an informed
decision on which one to use.  Also what are their policies on the
relevance of keywords - e.g. if I had cabbage.com, would they force me
to show only ads bidding on the keyword cabbage, or could I show ads
for the keyword casino.