Here is a list of resources for Unix and GNU/Linux bootloaders:
GRUB Legacy: The original GRand Unified Bootloader. Now known as GRUB Legacy.
GRUB: The latest and greatest. More commonly known as GRUB2.
BRUG: Brand-new Universal loadeR from GRUB. Based on GRUB. Adds features like new object format and configurable menu system.
LILO: LInux LOader. The original GNU/Linux bootloader.
Coreboot: An open source BIOS.
UEFI: Unified Extensible Firmware Interface. Previously known as EFI. Apple uses a variant of this.
PXE: Preboot Execution Environment. Boot over a network.
Syslinux: Syslinux, PXELinux and ISOLinux resources.