user317: I'd like to buy a mining rig, something like 4 5850 cards, preferably more.  I'd rather not build it myself.  Are there any vendors who sell such machines at a reasonable price?

user5: There are two sites that I know of: bitcoin-rigs.com and bitcoinrigs.com
If you have a local computer shop near you, you could also order the parts and ask them to mount. There is a wiki entry for mining rigs that has a few standard configurations (including two setups with 5850s).
You might also want to check the Marketplace section of the bitcointalk forums. Sometimes people sell used rigs there.

317: <p>I'd like to buy a mining rig, something like 4 5850 cards, preferably more.  I'd rather not build it myself.  Are there any vendors who sell such machines at a reasonable price?</p>
 5: <p>There are two sites that I know of: <a href="http://www.bitcoin-rigs.com" rel="nofollow">bitcoin-rigs.com</a> and <a href="http://www.bitcoinrigs.com/" rel="nofollow">bitcoinrigs.com</a></p>

<p>If you have a local computer shop near you, you could also order the parts and ask them to mount. There is a wiki entry for <a href="https://en.bitcoin.it/wiki/Mining_rig" rel="nofollow">mining rigs</a> that has a few standard configurations (including <a href="https://en.bitcoin.it/wiki/Mining_rig#Two_ATI_5850s.2C_Approximately_600_Mhash.2Fs" rel="nofollow">two</a> <a href="https://en.bitcoin.it/wiki/Mining_rig#Three_ATI_5850s.2C_Approximately_900_Mhash.2Fs" rel="nofollow">setups</a> with 5850s).</p>

<p>You might also want to check the Marketplace section of the <a href="http://bitcointalk.org" rel="nofollow">bitcointalk</a> forums. Sometimes people sell used rigs there.</p>
