Another thing is many RPGs imply you should roll those hit dice. Sure, they all provide average HP, but it feels somewhat mendacious to use that number.
So for a while I used the cross-off system. For each hit die the creature has, you can assign it a wound box or space or something. When a PC hits your monster, note the damage of the attack. 4 or less means you do a slash through a box. 5 or more mean you do an X. If you already have a slash and you would have to apply another slash, do it in the opposite orientation and you've got an X. All boxes being xed means the monster is dead. Simple. I still recommend it.
But what I've been doing for a couple years is using dice as psuedo-minis to keep a theater of the mind laid out. It's great for running online games. It's also a way to track HP. With 1HD creatures you can literally roll the HP and see how healthy your monsters are. With higher toughness creatures I usually give them a series of hits, like the hit boxes mention above. For instance, a three d8 monster would probably have about six hits on it, so I can just turn it to the six side. Or I could turn it to the 3 side and take it down a pip whenever the monster has suffered two weak blow or one strong blow. I kinda fluctuate in my methods. I've pulled out d10s and d12s to take care of even tougher monsters too.
Here's a pic of an actual fight:
Here's another detail:
This player (one Derrek played by one John) has ensorcelled a baddie since the last picture. It is now at the top of the picture, to the north of another monster, to show that it is attacking its former comrade. Note also Derrek has a couple hash-marks on his sheet to keep track of how long that charm spell is going to last.