Multiboot Option Reference by brands

HP/Compaq - Esc (starting to use F9 also) (F10 will usually access BIOS)
Dell - F12  (F2 will access BIOS)
Gateway/eMachines - F10 (moving to F12 with newer models)  (F2 will access BIOS)
Acer - F12 (not always)  (F2 will access BIOS)
Toshiba - F12 (older systems will be different)
Sony - usually will boot to CD, may ask you to "Press any key to boot from CD"
Asus - Esc (F2 will access BIOS)
Samsung -  Esc (F2 will access BIOS)