Storage – Boring but Important
Don't tell Allyn we said this, but storage is b-o-o-o-o-o-r-i-n-g! Actually, it's one of the more interesting avenues of change in PC hardware in the last 5 years and with NVMe SSDs now reasonable priced from vendors like Intel, Samsung, and others, getting mind-bendingly faster storage is within reach to use as your primary or your only system drive.
The current "best of the best" is the Samsung 960 Pro though the 960 EVO is a close second and will save you quite a bit in terms of cost per GB. You can pick up the 960 EVO 1TB drive for $479 on Amazon or as low as $129 for the 250GB model if you plan to supplement with spinning drives.
If you are looking for a lower cost solution, but still want to keep it all on solid state, might we recommend the Samsung 850 EVO SATA, where the same 1TB capacity runs slightly less expensive at $324.
Finally, for your spinning disk, multi-terabyte needs, Allyn still likes the Western Digital Red drives for RAID configurations (and don't you deserve redundancy protection?).
Cases and Cooling
Whether you are starting from scratch or just need a new case for your system, it's hard to argue with the value proposition from Corsair's Carbide series. The 100R comes in just a hair under $60, and is a solid mid-tower with good build quality and features for the price.
For a step up the options are vast, but sticking with Corsair for this example yeilds the excellent Graphite series, with the full-tower 780T a nice addition to the family that includes the older (and still awesome) 600T.
Let us not forget about CPU cooling, which is a market with as many players as the enclosure category. I'm a fan (pun intended) of air cooling for most of my builds, but there is no denying the power of a big dual-width liquid cooler for overclocking. Corsair has long been a go-to, but we shouldn't forget about Cooler Master, with very good performance and low noise output from their MasterLiquid Pro 240 and 280; and these are priced very competitively.
It wouldn't be a cooler recommendation without the long-time #1 seller: Cooler Master's Hyper 212 EVO. This is still one of the best coolers you can buy for $30, and represents a huge step up from most stock heatsinks.