28mm War of the Roses/Late Medieval Europe 1450 onwards - Perry Miniatures do plastics to back up their smaller range of metals, so an infinite variety of figures. About as cheap as you'll get while being top quality figures.
20mm Medieval is not my bag, but 'Paul' on here has quite a few. Again they are mostly plastic, but there's quite a variety in what he's shown here.
These might wet your appetite;
Some Serious Eye CandyCaptain Blood's WotRSilent Invaders WotR - There's a link to his rules some where in there.
I could be here all night to be honest, there are a number of threads in the pages of this board of equal standard...
If 'Skirmish' gaming isn't your thing, I gather 'Impetus' are a popular rule set for actual battles... but I don't know anything about them to be honest.