There's a few sites that offer this service out there but by far the best is MiningRigRentals! They not only have a great interface but offer excellent support, if you don't get the advertised hashrate or the server goes down you don't pay! And there are some real money makers on here! 
 

 
The rental above was .22 btc for the day.. about $50 US. Over a 3 day period it brought in .7 BTC/day! Almost 1/2 BTC in profit a day!! There's a few of these kind of rentals floating around their site, some babysitting may be needed as the larger the hashrate the more errors can occur and it will switch or disable what it thinks to be a faulty pool, but you can add multiple servers as backups. Now onto the large hashrate, let me explain a little here, with MiningRigRentals the owners putting up their rigs for rent can point as many miners as they have to one "rig" which can lead to some funky hashrates. 18TH/s is probably the normal combined hashrate for all the individual miners, and based on the difficulty settings the pools were spitting back to me it's a whole lot of 100 TH/s miners.. A WHOLE LOT! I was basically getting oc/burst speeds on every miner attached to this rig. This seems to happen more with the larger rigs (over 10 TH/s), but all it takes is the right server! Luckily Bitcoin Affiliate Network (PPS Pool) has a testing server for large miners, and numerous servers throughout the world, it says fixed 8096 difficulty but it only spits out a low difficulty. The hashrate goes between an astonishing 40-80 TH/s in this case (on basically every other server I was getting 24 TH/s max due to the variable difficulty giving out too high of a result). So really just play around with servers until you find a good match. The site also gives you a graph (as pictured above) up to 2 weeks of previous hash-rates so you can shop around for a goodie.
 
They also listen to your advice! Check out this new feature I requested, a rented vs running hash-rate