State if it's cross platform or not, freely available, or not, etc. Whatever you know about it.
So far I like the following combos:
"Ariel" BOLD: 9, 10, 11, 12
"Ariel" PLAIN: 9, 12
"Courier New" BOLD: 8 (didn't try more...)
And dislike the following:
"Ariel" BOLD: 6, 7, 8, 14, 16, 18, 21
"Ariel" PLAIN: 6, 7, 8, 10, 11, 14, 16, 18, 21
Microsoft-only fonts such as Calibri and friends aren't welcome/useful here.
What I'm especially looking for is the smallest possible good looking font combo. Something that looks good fairly big would be nice, too.
Some examples:
Ariel BOLD 10 :

Courier New Bold 8 :

Ariel 12 BOLD:

Fred.