Hoo boy, I use my share of variant rules.
First, I use a hit point/wound point system. Your hit points heal at a rate of 1/level/hour. You also have wound points equal to your Constitution, which heal at a rate of 1 per day of bed rest. If you run out of hit points, you start taking wound point damage. If you have any WP damage, you suffer a -2 penalty to attack rolls and saves. When you reach 0 WP, you are disabled, and at -10 WP, you're dead.
Most chump bad guys go down as soon as they take any WP damage, which leaves them alive for interrogation and also allows fighters to cleave and such. Of course, big critters usually rely more on WP than HP. Healing spells heal 1 WP for every die of HP healed. The same applies for damage from Inflict spells.
I still use existing rules for poisons, but only because I haven't found any good ones I like yet. I'd prefer if poisons functioned as they do in real life. Some would kill nearly instantly, but most stay in your system and damage you over the long run. I don't like how you can have a PC ingest a tranquilizer poison and have him just ignore it completely, when logically even the most hardy folks would eventually pass out.
I also am slowly trying to phase out core D&D spellcasting classes, and introduce the Elements of Magic class Mage.
