System Commander
System Commander is a boot menu, written by V-Communications (the Sourcer guys). It has evolved into a quite complex bootmenu that does auto partitioning and other nifty tricks.
It can boot anything from BeOS, FreeBSD, Win98 and Windows2000.
It supports heaps of various operating systems and file systems.
It doesn't load custom kernels and such, but you can use it as your master bootmenu, and install GRUB on a secondary partition and have System Commander boot GRUB!