I tell players when a monster is bloodied (as required for lots of rules)
and also frequently announce when a monster is "Clinging to life" sometimes with a graphic description of a nearly severed limb, disembowlment, etc.
Clinging to life is notoriously vague, but it serves as an encouragement to stick to a low damage power, either an at-will or automatic damage. One of the players tried to peg it down to 10% remaining heath, but it is far more random and arbitrary than that.

And I usually let a free Heal check tell more, like who's the most or least hurt or the 1/4 and 3/4 points. This will often come up with a PC wanting to know if it's worth it to throw healing on an unbloodied PC, or which of several bloodied monsters to try to take out first.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.