When I was reading the Point-Buy system for the attributes, I thought of another system that could also work really well. I personally like having characters that have penalties to help make their bonuses seem that much better. My proposed system works with the standard fantasy tier.
The character's attributes start at 10 and they buy their attributes at a rate of 1:1 just like the 3P system. The difference is that they can only get an attribute to a maximum of 15 without a penalty. If they wish to use more points to get an attribute higher than that (to a maximum of 18 before racial modifiers), they must have an equal number of attribute points below 10 to offset their character's greater power. This point penalty can not be fixed during character creation.
Example:
I've created a half-elf sorcerer with the ability scores of STR 10/DEX 15/CON 12/INT 13/WIS 10/CHA 15. If I wanted to raise my CHA score higher than 15, I must take an equal number of points below 10. This could result in either my STR becoming 7, my WIS becoming 7, or some blend between the two attributes that totals 3 points (ex. STR 8/WIS 9). I could not take it out of my other scores because they are already over 10 and the penalty would not be as noticeable if you could reduce it during character creation.
This is just an idea I have been working on since I first saw the Point-Buy system for 3.5E. I just wanted to post it as an alternative to the systems that 3P already offers because I felt that 3P's Point-Buy had the same problem: the only penalty to a character increasing their score to 18 was that there was less points to spend on other scores. That did not seem like it was strong enough to warrant the characters getting such a powerful score.