I've seen this topic come up many times but just realized I have a pretty concrete answer. I recently purchased a few Dynex UPS's that came with excellent power monitoring software. Off the top of my head, I can show how much power is being used by 2 of my crunchers (with monitors on of course):
Athlon XP 2500+ @ 2150MHz
nForce2 Ultra
420w TSP Power supply
17" Samsung LCD
GeForce 3 Ti500
1GB RAM
Audigy 2
Raptor 36GB
Seagate 80GB
CDRW drive
DVD ROM drive
Total UPS draw = ~245 watts
UPS draw without LCD = ~211 watts
Pentium 4 2.53@2.70
Intel 845
420w TSP power supply
2x512MB OCZ
17" Dell Trinitron CRT
ATI 9700 Pro
20GB WDC
40GB Maxtor
CDRW drive
DVDROM drive
Total UPS draw = ~ 270 watts
Athlon XP 2500+ @ 2150MHz
nForce2 Ultra
420w TSP Power supply
17" Samsung LCD
GeForce 3 Ti500
1GB RAM
Audigy 2
Raptor 36GB
Seagate 80GB
CDRW drive
DVD ROM drive
Total UPS draw = ~245 watts
UPS draw without LCD = ~211 watts
Pentium 4 2.53@2.70
Intel 845
420w TSP power supply
2x512MB OCZ
17" Dell Trinitron CRT
ATI 9700 Pro
20GB WDC
40GB Maxtor
CDRW drive
DVDROM drive
Total UPS draw = ~ 270 watts