My current PC is built out of the following:
CPU - Celeron 336, with stock cooler (which gets loud when pushed)
Motherboard - Intel D945GTP (VRM gets hot and fuxx0rs certain RAM addresses)
RAM - 4 * Apacer 512MiB DDR2-533 (a.k.a. "PC2-4300" though that should really be "PC2-4266")
HDDs - 2 * WD800JD-00LSA0 (quiet, no problems to date) and 1 * ST31000528AS (firmware CC38) (noisy, used for large files that aren't as frequently accessed)
Optical drives - Lite-On SHM-165P6S and Sony CRX320EE
PSU - Hipro HP-D3057F3H with capacitors and fan replaced
Case - made by AOpen, but I don't know which model; pathetic fan grilles (the type with lots of small round holes)
Fan - NMB 3110SB-04W-B40-E00, installed in one of the exhaust fan positions (with the original grille broken away and a wire grille installed - far better airflow this way)
The motherboard would be the first target, as it doesn't work the way it should. A better case would also be nice - preferably with a bigger fan (not two in parallel) and support for at least four HDDs.
If I get something like a WD3200KS, I may consider double-partitioning it and swapping it in place of the two 80GB drives, but it's unlikely that I will. I don't intend on getting an SSD any time soon as the internet connection is the real slow part.
The installed OS is Windows XP Home SP3. I'll say more when I want to.