I personally very much like lshw (and its gui version). In addition to the bios (DMI table) info on hardware that you also get from dmidecode, it can gather information from e.g. /proc, /sys or /dev (depending on the platform of course) and will query pci/agp, usb, ide and more to add to the picture. It also can give ouput in html or xml form if you need it.

I do use dmidecode as well, though.