The best icons I found for these features are the ones from Dolphin Smalltalk (now opensourced ;-) )

>
> for me they are not small, but misplaced. I expect to have them close to
> where I���m looking for: the code (that happens in all debuggers I know, with
> the exception of ddd who opens a different window).
> For me, they should be in the code panel and not in the stack panel.
> also��� shortcuts do not work in code panel :(
+1 to this. Altough if you use shortcuts you don't care where they are located.
BTW, is it possible to use the function keys as shortcuts? I would map F10-F12 (with modifiers) as shortcuts.