It's interesting that this comes up now, since I've just built two Win7 PCs in the past few weeks to replace our XP machines (the install on mine is from June 2008).
Changing prices between when I bought the parts for the first (top) one and those for the second account for most of the differences between them. Both are built in Fractal Design ARC Midi R2 cases.
Top:
Gigabyte Z87X-D3H
i3 4130 Haswell
16 GB Crucial Ballistic Sport DDR3 1600 9-9-9-24
MSI R7 260X video card
Samsung 840 Pro SSD - 128 GB (too small!)
WD Blue 500 GB
Rosewill Capstone 650-M PSU
HT Omega Claro II
Cougar 140 mm PWM fans
Samsung DVD writer
Win7 Home Premium 64
Bottom:
ASUS Z97-A
i3 4150 Haswell (refresh)
16 GB Crucial Ballistic Sport DDR3 1600 9-9-9-24
MSI R9 270 video card
Samsung 840 Pro SSD - 256 GB (I learned my lesson!)
WD Blue 1 TB
Seasonic SSR-650RM PSU (Rosewill cables are usefully longer)
HT Omega Claro II
Cougar 140 mm PWM fans
LG DVD writer
Lite-On DVD reader (old)
Win7 Pro 64