Artificer. He takes their magic items and absorbs the XP from them, then crafts wands that contain their spells. He builds himself a +1 force impact light crossbow, that there's his mini cannon. He uses wands to fire his mega shots. He buys a wand sheath and wand bracelets, for a total of 11 wands at any times he wants. Rod of many wands is awesome, since you can fire several spells at once.

I think that Artificer is the best megaman class. It doesn't quite have the flavor down pat, but it's definitely the strongest, and you can build yourself an arm cannon, and get the special abilities of almost any spellcaster. That spellthief idea is pretty sweet too.