CPU-Z is a freeware that gathers information on some of the main devices of your system.

CPU
Name and number.
Core stepping and process.
Package.
Core voltage.
Internal and external clocks, clock multiplier.
Supported instructions sets.
Cache information.

Mainboard
Vendor, model and revision.
BIOS model and date.
Chipset (northbridge and southbridge) and sensor.
Graphic interface.

Memory
Frequency and timings.
Module(s) specification using SPD (Serial Presence Detect) : vendor, serial number, timings table.