There seems to be alot of big fish in the pond !
BuyDomains, NameAdmin, Marchex, Eliqua, Chris Chena, Internet REIT are a few I have heard of - There will be many more.
Some of these people spend in excess of $100,000 per name - and often too

Bonkers seems to be one of the biggest spenders recently.
I'm sure there are many more - interesting article
http://www.startupjournal.com/ecommerce/ecommerce/20051118-kesmodel.html
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Internet REIT (iREIT), a leading supplier of high-value Internet traffic to advertisers, has recently aquired Netster.com web portal and major portions of the Netster domain name portfolio. Netster is the latest in a series of strategic acquisitions for iREIT, which has acquired over 50 portfolios of Internet traffic in the past fifteen months, including such high-value domains as Bands.com, OfficeSupply.com and AfricanAmericans.com. The addition of the Netster portfolio gives iREIT more than 400,000 domain properties under management and brings the company’s total portfolio of traffic up to 50 million visitors per month.
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heres another one - Oversee.net
Oversee.net, a technology-driven media company, today announced it has acquired 10 domain portfolios over the last two months. The Company continues to aggressively build its portfolio of successful domain names and then quickly monetizes them.
Oversee monetizes more than one million domain names per month and has more than 100 million unique visitors per month. The Company owns DomainSponsor, the industry leader in domain monetization.
Commenting on the increase in transactions, Lawrence Ng, Chief Executive Officer of Oversee.net said, “Oversee has accelerated its program to purchase domain portfolios.
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