I was interested in a feature that is present in a lot of IDE. I don't know if this has a name or if there's a patent on it : when you instert a (, [ or {, a ), [ or } is automatically inserted you don't get unbalanced (), [] or {}
(setq skeleton-pair t)
(global-set-key "[" 'skeleton-pair-insert-maybe)
(global-set-key "{" 'skeleton-pair-insert-maybe)
(global-set-key "(" 'skeleton-pair-insert-maybe)
very nice :D