I have been using SearchKeys for a while now as I explore my mouseless computing world.  It's good because firefox just emits numeric shortcut keys for google search results and my bookmarks at del.icio.us (used to support google groups, too bad). 

SearchKeys shortcuts:

(number) - open link in current tab
, - previous results
. - next results
alt+(number or paging shortcut) - open in new tab

I learned about Hint-a-hint from  a blog post of boodhoo here and the thing that i love about h-a-h is for page navigation through controls.  It's useful when filling up a page information so you don't have to tab through all the controls.  One can easily select a dropdown, a button, almost any selectable control in the page (unlike searchkeys which is only for links).

Hint-a-hint shortcuts:

hold spacebar - display numeric shortcut keys
number - open in current tab
hold ctrl + number - open in new tab