THIS SITE, and even moreso
this site, give lots of good information on processors (including the voltage).
Here is a snip from the second link:
Celeron 800 - 800MHz (100x8.0) - 1.65v or 1.7v or 1.75v - 128KB L2 cache (Coppermine-128)
Celeron 850 - 850MHz (100x8.5) - 1.65v or 1.7v or 1.75v - 128KB L2 cache (Coppermine-128)
Celeron 900 - 900MHz (100x9.0) - 1.75v - 128KB L2 cache (Coppermine-128 - FCPGA or FCPGA2)
Celeron 950 - 950MHz (100x9.5) - 1.75v - 128KB L2 cache (Coppermine-128 - FCPGA or FCPGA2)
Celeron 1.0G - 1000MHz (100x10.0) - 1.75v - 128KB L2 cache (Coppermine-128 - FCPGA or FCPGA2)
Celeron 1.1G - 1100MHz (100x11.0) - 1.75v - 128KB L2 cache (Coppermine-128 - FCPGA or FCPGA2)
Celeron 900A - 900MHz (100x9.0) - 1.475v - 256KB L2 cache (Tualatin - FCPGA2)
Celeron 1.0A - 1000MHz (100x10.0) - 1.475v or 1.5v - 256KB L2 cache (Tualatin - FCPGA2)
Celeron 1.1A - 1100MHz (100x11.0) - 1.475v or 1.5v - 256KB L2 cache (Tualatin - FCPGA2)
Celeron 1.2G - 1200MHz (100x12.0) - 1.475v or 1.5v - 256KB L2 cache (Tualatin - FCPGA2)
Celeron 1.3G - 1300MHz (100x13.0) - 1.5v - 256KB L2 cache (Tualatin - FCPGA2)
Celeron 1.4G - 1400MHz (100x14.0) - 1.5v - 256KB L2 cache (Tualatin - FCPGA2)
Celeron 1.7G - 1700MHz (100x17.0) - 1.75v - 128KB L2 cache (Willamette - Socket 478)
Celeron 1.8G - 1800MHz (100x18.0) - 1.75v - 128KB L2 cache (Willamette - Socket 478)
Celeron 2.0G - 2000MHz (100x20.0) - 1.475v or 1.5v or 1.525v - 128KB L2 cache (Northwood - Socket 478)
Celeron 2.1G - 2100MHz (100x21.0) - 1.475v or 1.5v or 1.525v - 128KB L2 cache (Northwood - Socket 478)
Celeron 2.2G - 2200MHz (100x22.0) - 1.475v or 1.5v or 1.525v - 128KB L2 cache (Northwood - Socket 478)