Effective SPAM filter for stand alone exchange 2007?

I have just deployed an exchange 2007 server and the company gets a ton of spam..  The client would like me to recommend a product to minimize this without bouncing stuff they need.  Does anyone have the answer?
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Postini Junk E-mail & Spam Filtering  Cost is 1.00 per month per email address.  The exchange box is setup to only allow mail from the Postini servers & all mail routes through Postini.  This is a spam/virus filter that is adjustable at the domain level & user level.  Each user is able to login individually to manage settings & check the emails that are being blocked (if needed).  Postini authenticates the user account by popping the Exchange server using the password that is entered during login.

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We use Barracuda spam filters (model 400) and it has reduced spam significantly. It also blocks viruses. I've read some good things about Ironport even though I havent used it myself.
Vamsoft ORF has just released a version for 2007, $200 for the server irrespective of users, and does a fantastic job.  Key to this is Greylisting, which has done an amazing job getting rid of spam on my networks.

Did you know that you can add a built-in antispam agent without adding an Edge server:
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