I'm a big fan of hotkeys. The less I have to touch the mouse, the better. With this in mind, here are my favorite GoldMine hotkeys;
CTRL+SHIFT+E : Create a new e-mail to the current contact.
F3 : Search the current tab for text.
F4 : Bring up the Search Center.
F5 : Bring up the E-mail Center.
F6 : Activity List.
F7 : Calendar.
F9 : Opportunities.