My first build. Was aiming for relatively low budget while still achieving moderate performance and using reliable and reputable brands. By taking advantage of some good sales and rebates, as well as a couple of "used" parts from Reddit Hardwareswap, I was able to get a solid rig for a great price if I do say so myself. I bought the PSU, HDD, and case back in July and the rest of the parts in September.
Future upgrades - new HSF (don't really like the stock one, though it'll do for now), monitor (currently using old 19" TV), wireless adapter for convenience, optical drive/Blu-ray drive, SSD.
Part-by-part breakdown (All prices listed are after rebate):
CPU - Was aiming for an AMD quad-core and with a sale and subsequent 1-day 10% off Newegg promo, I couldn't turn away from the 4130. I'm sure I'll get criticism for not choosing either a 4300 or a 6300, but the price was too good to turn down and I don't think I really needed the extra 6 cores.
TIM - Was originally just going to use stock TIM on the stock HSF, but I had trouble initially mounting the fan and ended up taking it off and messing up the pre-applied TIM. So luckily I had this lying around after buying it when I reseated the HSF on my mom's Dell desktop.
MB - Bought this off of /r/Hardwareswap for relatively cheap in like-new condition; was never mounted before, only tested for POST.
RAM - Also bought off of /r/Hardwareswap - unfortunately had to wait for it as the last piece before building because it shipped from Canada.
HD - Got lucky by coupling a $15 promo code with a Shell Shocker deal = steal for a 1 TB HDD.
GPU - I had been planning on a 7850 since I first started planning to build a PC and this 2 GB version was perfect. Slightly above what I had allocated for a GPU, but I was willing to go a bit over for this. I only plan on gaming on one monitor at 1080p, so this has all the power I need.
Case - Was cheap and has a good number of features for being such a budget case - bottom-mounted PSU, all black interior, cable management options. Only came with one rear fan installed, so that's why I bought the additional 120mm fans. I only have one intake fan in the front installed, though I may install a top exhaust and side intake later on.
PSU - Cheap after I coupled rebate and promo code for $15 off (split between this and the case). Provides enough power for a single GPU, non-overclocked rig like I've got.
OS - Had an extra key after Dell gave a new key when my mobo on my laptop crapped out after a bad BIOS update. Ripped the iso from an install disk I have from my laptop and put it on an 8 GB flash drive and installed via USB. This also eliminated the need for an optical drive, though I may plan on getting one later anyways.
Mouse - Wanted to get a solid mouse to replace the random wireless Logitech one I have. It has adjustable DPI and 5 buttons and works really well.