Sniffer with WPA-decrypt (known passphrase)

I'm looking for recommendations (Linux or Windows) on a wireless
sniffer setup that can decrypt WPA Personal/TKIP with a known
passphrase. I have full control over the network so I can start the
sniffer before any other clients and I know the passphrase, etc.

Freeware would be preferred but I can spend some money.

Thanks,
Andrew