The Core i5-2500K is an overclocking beast that deserves (or demands) a better cooler than the freebie fan Intel throws in the box with its CPUs. I opted for the Cooler Master Hyper 212 Plus to keep my processor on ice, and it proved to be the best $30 I spent on my new rig. The Hyper 212 Plus keeps my overclocked CPU in the low 30s during everyday use. When gaming and watching a video stream, the processor barely cracks 40 degrees. Handbrake maxing out each core to 100% only hits 51 degrees Celsius.
There are obviously more powerful CPU coolers out there: a liquid cooling system could probably run circles around the Hyper 212 Plus. Those solutions also cost several times as much money. The Hyper 212 is quiet, cheap and supports a secondary fan for additional cooling. It also sits at the top of a bang-for-your-buck Tom's Hardware cooler chart.
I'd recommend the Hyper 212 Plus to anyone looking for an affordable aftermarket cooler next year. Hint: it's only $20 on Amazon these days. You could also step up to Cooler Master's brand new Hyper 212 EVO, which costs about 40 bucks.