SIW (System Information for Windows) is a free and full-featured tool for Windows which gathers detailed information about your system's software, hardware and network, and presents it in a very comprehensible manner. It displays everything from the CPU clock and technology to RAM frequency, BIOS and Windows version, license information for installed programs and a lot more.
It also offers a sensors feature to check on your components' temperatures, a password retrieval tool, and real-time monitors for processor, memory, page file usage, and network traffic. The end result can be exported as a report file to HTML, CSV, XML or text - the last three supported only in the paid version. Despite being loaded with plenty of features, SIW requires very little resources to run and retrieves information within seconds.
SIW can be downloaded with the Windows Installer or as a standalone program (use alternate mirror) that requires no installation, which makes it an excellent tool to have on your flash drive.