I want to buy between $5k and $10k worth of bitcoin, like yesterday.
Bank wire to an exchange will be your most economical.
Mt. Gox lets you do that, though for some amount they'll want you to verify your accoutn:
BITSTAMP is another.
And there are many more:
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http://en.bitcoin.it/wiki/Buying_bitcoinsYou could try also doing a transfer from Coinbase.
You might find someone local willing to trade.
Try multiple paths, including a local buy perhaps:
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http://www.LocalBitcoins.com