Best fonts for buttons, balloons, etc.?

I need some input...

What are your favorite fonts to use for graphic buttons, labels in images,
etc.?   

In particular, I am doing an imagemap which will have to have a number of
labels on it in "balloons".  I need to choose a font that will be highly
legible, anti-alias well, in as small a size as possible, to avoid covering up
as much of the image below as possible.  Suggestions?

TIA,

--Bill

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