Current Gaming Build - Upgrades

PCPartPicker part list / Price breakdown by merchant

So this is my current gaming build and I have a $300 budget. I was wondering whether you guys could recommend anything useful for the build within that budget?

CPU: Intel Core i5-4690K 3.5GHz Quad-Core Processor ($224.95 @ SuperBiiz)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($24.88 @ OutletPC)
Motherboard: MSI Z97-GAMING 5 ATX LGA1150 Motherboard ($144.88 @ OutletPC)
Memory: Corsair Vengeance Pro 16GB (2 x 8GB) DDR3-1866 Memory ($69.99 @ Newegg)
Storage: Samsung 850 EVO-Series 500GB 2.5" Solid State Drive ($151.89 @ OutletPC)
Storage: Hitachi Deskstar 7K2000 2TB 3.5" 7200RPM Internal Hard Drive
Video Card: MSI GeForce GTX 970 4GB Twin Frozr V Video Card ($324.99 @ B&H)
Case: Fractal Design Define R4 w/Window (Black Pearl) ATX Mid Tower Case ($109.99 @ SuperBiiz)
Power Supply: SeaSonic 650W 80+ Gold Certified Fully-Modular ATX Power Supply ($111.99 @ SuperBiiz)
Optical Drive: LG GH24NSC0B DVD/CD Writer ($15.89 @ OutletPC)
Operating System: Microsoft Windows 10 Home OEM (64-bit) ($87.95 @ OutletPC)
Monitor: Acer GN246HL 144Hz 24.0" Monitor ($207.58 @ Newegg)
Total: $1474.98
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-02-08 13:41 EST-0500

http://pcpartpicker.com/p/6DGWxr
 
Solution
If you like the aesthetics, individually slaved cables that matches the color of your build. Bitfenix and lot more brands sell cables like this. Aftermarket case fans, like Corsair SP. A fan controller to control fan speeds, for example NZXT Grid+. Perhaps also the NZXT Hue if you like LEDs? Performance wise your build seems fine! Perhaps you could improve your peripherals? Mouse/keyboard or headset?

RCFProd

Expert
Ambassador
If you like the aesthetics, individually slaved cables that matches the color of your build. Bitfenix and lot more brands sell cables like this. Aftermarket case fans, like Corsair SP. A fan controller to control fan speeds, for example NZXT Grid+. Perhaps also the NZXT Hue if you like LEDs? Performance wise your build seems fine! Perhaps you could improve your peripherals? Mouse/keyboard or headset?
 
Solution
For $300 I don't think there is any meaningful step up from where you are...that's a pretty solid build.

(edit) Of course like RCFProd mentioned, aesthetics....I prefer black on black with varying shades of black....flat black preferably, really makes the black stand out more ;P