http://www.rootkit.com http://www.chkrootkit.com http://www.antirootkit.com http://www.invisiblethings.com
Look for rootkit revealer in Google as well.
Types of rootkits
class, kernel mode, loadable (kernel modules, memory based, persistent rootkit, user-mode rootkit, vendor rootkit, virtual machine based rootkit (VMBR).
askmeaboutlinux 