PC World has compiled a list of free, but powerful applications for Windows users. Here is their list and a link to the details below.
Sysinternals Suite: Monitor programs run during bootup, Process
Monitor, Process Explorer, RootkitRevealer, and more.
HWiNFO32: Comprehensive hardware diagnostics and inventory tool.
Crap Cleaner: Clean up after Windows.
Recuva: Locate and selectively restore deleted files.
FileZilla: FTP client.
Virtual CloneDrive: Mount ISO images as virtual CD/DVD drives.
Defraggler: Defragment individual files or an entire hard disk.
ImgBurn: Burn ISO images to disc, and build images from files & folders.
7-Zip: Compression utility.
VirtualBox: Desktop virtualization for free. Think VMWare.
Check out the full article from PC World at this link.