axeman 221 :
I have the Cooler Master N300 and I use the two fans that came with it. I have one fan in the front that draws air in and a fan in the top-back that blows it out the back.
The N300 has huge cooling potential, but with one intake and one exhaust, you aren't exactly taking advantage of it. At minimum, I'd put another fan in the front, and turn all the fan speeds up, fast enough so that they move air, but just slow enough that they aren't painfully loud to listen to. Optimally, I would fill both front fan slots as intakes as well as one on that side by the hard drive cage if that space isn't filled by hard drives, one exhaust in the back, and another exhaust in the top as far back as possible. If you have the non-windowed version of the N300, I'd put a fan on the side panel pointed at the GPU instead of the one next to the motherboard. With a GPU this hot, evacuating the heat from your case becomes even more of a priority.
On top of that, a better CPU cooler won't hurt. Even the cheap Hyper TX3 will keep the i5 4460's temps under check. I get a maximum of 55C under full load with mine. If you want a quieter CPU cooler, the Hyper212 or the Cryorig H7 with their 120mm fans will help. If possible, with any of these tower coolers, I'd mount them horizontally with the fan blowing up instead of sideways, helping vent the heat from the graphics card and following the natural path of heat rising. Combined with a top-mounted exhaust fan, this will in turn raise your CPU temps a bit, but it'll help evacuate the heat inside your case even faster, and keep temps more stable in the long run. Keep the fan between the heatsink tower and the top of the GPU for maximum effect.
All of this depends on how much you want to spend. In terms of least to greatest expenditure:
1.) one extra case fan
2.) one extra case fan and a cheaper CPU cooler
3.) one extra case fan and a slightly more expensive CPU cooler
4.) more extra case fans and a slightly more expensive CPU cooler
To be fair, you shouldn't be spending more than $50 maximum. Make sure you have the motherboard headers or necessary splitters to have all your fans plugged into the motherboard so you can control their speeds.
Holy essay :O