Hard to say for me. I started out building a 486SX/33, and upgraded it bit by bit, going through a 486DX, P200MMX, Celeron 300A, P3 500@620, Duron 700, Duron 1G to what I have now:
AMD AthlonXP 1700+ @ 1.62ghz (147mhz FSB Multiplier unlocked but not changed)
ECS K7S5A with onboard LAN (rev. 3)
512MB Crucial RAM (PC133@147)
Coolermaster X-Dream Heatsink (on CPU)
Pioneer 16x DVD ROM - Slot loading
8x4x32 CDRW
Samsung 48x CDROM
Creative Sound Blaster Live! 1024
Samsung 30gb hd
WD 40gb hd
Fujitsu 20gb hd
Ati Radeon 32mb SDR (180/180)
Longshine Ultra-ATA controller (CMD-649U chip)
350W PSU
All running Gentoo Linux of course.
As you see, I have some good parts and some bad (most notably the mobo and gfx card

)
But now I have some DDR, I can upgrade to an enthusiast-class board again. If only I still had that KT133A board, but the caps blew up.