While classic air cooling is still the solution of choice for most when thinking about building a new PC and stopping your CPU from overheating, there's always the option of liquid cooling. It's especially useful if you're going to be overclocking and pushing your hardware beyond its normal limits. It can be expensive to liquid cool your PC, but there are affordable options out there. For example, CCL Computers currently has a Cooler Master Seidon 240V all-in-one cooler for £49.49.
I actually wish it cost the round £50, because then it would qualify for CCL's free delivery. If you're looking to save an extra couple of quid, add something worth less than £3.95 (the price of delivery) to your order to push it over £50, an ethernet cable for instance.
As for the cooler itself, it's an all-in-one system, which is always handy if you don't want to be fiddling around with custom loops. Plus, as mentioned, it's one of the more affordable liquid cooling options on the market. It's also got a decent build quality, and it's quiet, which is always an important thing to consider with your cooling solutions. In addition, it's lit with blue LEDs, if you're into the internal designs of your PC. While we're on the topic, if you're looking to light up your PC but don't know where to start, we've got a beginner's guide for you right here.
Under £50 for liquid cooling is a good deal, and the Cooler Master Seidon 240V isn't often down below that. Worth a look if you're on a budget.