I've been using a Continuous Time Combat System in my campaign . It's a bit more complicated than your standard, abstract system, but I've grown to like it a lot. It's pretty easy to get used to. Here's how it works:
Roll your starting initiative (d10). Subtract dex reaction modifier. Minimum 1. That's when you start to act.
If you want to move, add time based on how far you are moving. This is your movement time. For characters with a movement rate of 12, add 1 for each square/hex you move. For characters with a movement rate of 6, add 2 for each square/hex you move.
Add 1/2 weapon speed or casting time. If you are a specialist mage casting a spell from your specialty school, subtract 1 from the casting time (minimum 1). If you have an attack bonus from magic or strength or whatever, subtract this bonus from your weapon speed (minimum 1). This is either casting time or attack swing. When this number of phases have passed, you make your attack roll, or your spell resolves. This is when spellcasters can be interrupted. Note that the weapon speed numbers can be precalculated before combat even begins, and recorded as modified weapon speeds. This isn't slow!
If you get multiple attacks, add 1/4 weapon speed after you make your first attack. When this number of phases have passed, you make your attack roll.
When your actions are done, re-roll initiative (modified by dex, minimum 1). We've been going back and forth between using a d10 and a d6 for this initiative. I greatly prefer d6.
There is no end of round or whatever. The phases keep counting up. If you have spells of duration measured in rounds, multiply that number by 10, and that's the phase that the duration ends on. Turns - multiply by 100.
The reason the weapon speeds were halved and quartered was to align weapon speeds more with spell casting time. It was felt that mages were too powerful under this system if full weapon speeds were used.
Comments on this system are welcome. If you think it's too slow and cumbersome, you should try it. It's really not that slow. It just takes some getting used to. For the players, it takes a bit to get used to rolling an initiative when your action is complete. For the DM, the hard part is jotting down numbers in order and tracking who goes when. For combats, the number of phases can go over 100 easily.
Here are some files, courtesy of Hans Neser, that you can use with the CTCS:
Time Unit Tracking Sheet for a Player (Word 97 format)
Time Unit Tracking Sheet for a DM (Word 97 format)