Here's a great youtube video that teaches a modern slice:
http://www.youtube.com/watch?v=II7Wo0y6fC8
Some folks here take great issue with this form, but it is the form currently used by just about every top pro. It produces a shot that stays incredible low after the bounce, has great penetration, and can have a nasty side ways slicing action depending upon the contact point (the lower it's hit, the more it slices to the side).
I've implemented the suggestions in this video into my bh slice. I've been able to add pace, consistency, and more spin to my bh slice. I'm more agressive with the shot than I had been.
One of the keys is that you need to set the racquet plane at the beginning of the forward stroke and then maintain that plane through the swing. Do not open or change the racquet face's angle at or after contact. Another key is that you allow your arm to naturally pivot around your shoulder. Higher balls will be mostly backspin. Lower balls will have a lot of side spin.
Your slices need to be pretty close to the top of the net to be effective - say around 1 foot. I agree with the folks that have said that you're looping them over and they're landing long. Even if they didn't land long, with that much net clearance they won't have any bite. They're just going to sit up in the court and a good player will punish them.
One thing that gets de-emphasized with this form a bit but is still important is that you still have to have hit through the ball to some degree. The shot is not a floater. It has as much pace as is possible and still have the ball land inside the baseline. When the shot's hit correctly it clears the net by less than a foot, lands about a foot or two inside the baseline, bounces up less than foot, and has some degree of side slice action along with the backspin. As you're watching this shot come toward you and you're moving to it, it's really difficult to know exactly when the ball will touch down so it makes it really difficult to time your stroke to hit it. All the while it's also slicing into your backhand (or away from your forehand), so you have to allow for that too.
Again, I'll acknowledge that some folks think that this current form is really a bad thing, but it is the form used by most pros and I've personally found it be highly effective.