I'm in love with microsystems myself, and so default to Roll for Shoes as a base whenever I'm creating something. It allows players to quickly develop their own skills during play according to what your character rolls well doing. It's great for lighthearted on-the-fly improv; I've welded it onto other systems in the past as the skill component.
Another personal favorite: Fate. Uses what are effectively d3s known as Fudge or Fate dice to fine-tune the curve of each roll. And the Aspects system allows great (and fast) character customizability.
Anyways, big scary dinos go rawr stomp chomp chomp but why can't you be a dino? I plan to incorporate this element, probably to the exclusion of human PCs, because humans are boring and puny and DINOS GO RAWR STOMP CHOMP. Maybe a roleplaying "remake" of The Creature That Ate Sheboygan?