Tom,
I have a method that actually does do what you want. I have found that the "grit" you speak of does not come from the bell curve, but rather holding the player to the stats he rolls and the order of the rolls. I use the 4d6 drop lowest, but the rolls have to be made in order as stated on the character sheet. Each player has to make 3 declarations before rolling begins:
1) What character sheet he/she will use. The NG 3.5 sheet has a different stat order and I allow people to use whatever char sheet they feel is the best. Not allowing rearrangement is essential.
2) The race of the character. No picking the race after you have rolled to boost a lower stat. You take what you get. Role with it!
3) The class of the character. Again, the key term here is "role with it." Your stats may be entirely in appropriate for the chosen class. How you overcome this is part of the fun.
When they have made their declarations, they then roll.
Now there is one thing that I allow them. In the PHB there is the rule that if the modifiers total -1 or less, then the player can reroll. I raise or lower this threshold. I have found that +2 gives the players somthing to work with, but does not make them too powerful. Here are some examples (from an NPC I was working on last night):
1/2 Elf Ranger
12 +1
13 +2
10 --
9 -1
6 -2
6 -2
7 -2
18 +4
12 +1
16 +3
12 +1
10 --
I stopped after the second set. Heres another example, I only rolled for this once:
Orc Sorcerer
14 +2
15 +2
13 +1
9 -1
8 -1
11 --
For this guy he is either gonna have to get a lot more charasmatic (NO ONE CALLS GROG UNCRASAMATIC!) or multiclass out. Though he can learn to do a lot if he takes metamagic feats. At 7th level this guy is still pretty dangerous with a mix of maximised, quickened and empowered spells. (28 points from a magic missile, and he can cast 2 in a round with one being quickened, thats 56 points!) And getting close to him might be a problem too. At 8th level its "Lightening bolt! Lightning bolt! Lightening bolt!"
Aaron.