1. 50%: Complete 50 achievements as quickly as possible
2. 98%: Complete all achivements sans 60 seconds
3. Century%: Complete the Century Achievement.
4. Number%: Complete all number related achievements.
5. Paint%: Get the Complete Makeover achivement.
6. 100 Times: Complete the game 100 times.

Portal

Achievement Unlocked

Suggestions for Category Extensions in Achievement Unlocked

Im probably wrong but...