Your distribution's list is the best way to tell if a piece of hardware will work when you first install Linux. Products listed on other hardware support lists may require manual configuration or a software upgrade.
Links:
[1] http://www.tldp.org/HOWTO/Hardware-HOWTO/
[2] http://www.linux-laptop.net/
[3] http://tuxmobil.org/
[4] http://gentoo-wiki.com/Index:Hardware
[5] http://www.linspire.com/linspire_hardware_compatibility.php
[6] http://club.mandriva.com/xwiki/bin/view/KB/HardwareIndex
[7] http://www.mepis.org/docs/en/index.php/Hardware
[8] http://docs.pclinuxos.com/index.php?title=Hardware
[9] https://hardware.redhat.com/
[10] http://hardwaredb.suse.de/
[11] http://www.turbolinux.com/products/compatibility/index.html
[12] https://wiki.ubuntu.com/HardwareSupport
[13] http://www.alsa-project.org/main/index.php/Matrix:Main
[14] http://www.linuxprinting.org/database.html