I've found the "pre-made" implants to be pretty useful for getting a stat high enough to put in another implant, or equip better armor. So, I compiled this list.
Here's how it works.
The first column, x/y/z, is the amount a stat is raised by using the QL 10/QL 20/QL 30 implant. Then comes the profession machine it is located in, and the implant type. Finally, the stat in (parenthesis) is the stat used by that particular implant (handy if you want to raise your Agility and have plenty of Intelligence, for example).
QL 10 implants require 24 in the stat, QL 20 requires 44, and QL 30 requires 64.
There are plenty of "duplicates" - sometimes different professions have the same implants, raising the same stat and requiring the same stat. Those I eliminated, and only included one. I didn't eliminate the ones that required different stats, for the above reason.
Agility
3/4/5 Adventurer Waist (Sense) *
4/6/7 Engineer Feet (Agility)
7/10/12 Meta-Physicist Leg (Stamina) *
7/10/12 Engineer Leg (Agility)
Strength
3/4/5 Trader Chest (Stamina) *
4/6/7 Doctor Left Arm (Stamina)
4/6/7 Martial Artist Left Arm (Strength)
7/10/12 Martial Artist Right Arm (Stamina)
Sense
3/4/5 Martial Artist Head (Sense)
3/4/5 Enforcer Head (Agility)
3/4/5 Adventurer Head (Intelligence) *
3/4/5 Agent Head (Psychic)
4/6/7 Adventurer Waist (Sense)
Psychic
3/4/5 Fixer Ear (Intelligence)
7/10/12 Fixer Head (Intelligence)
Stamina
3/4/5 Doctor Waist (Sense)
3/4/5 Soldier Waist (Stamina)
4/6/7 Meta-Physicist Leg (Stamina) *
7/10/12 Trader Chest (Stamina) *
Intelligence
3/4/5 Meta-Physicist Ear (Intelligence)
3/4/5 Nano-Technician Ear (Sense)
4/6/7 Engineer Eye (Intelligence)
Computer Literacy
4/6/8 Nano-Technician Right Hand (Intelligence)
4/6/8 Trader Right Hand (Agility)
6/9/12 Nano-Technician Eye (Intelligence)
Map Navigation
6/9/12 Adventurer Head (Intelligence) *
10/15/20 Trader Eye (Sense)
* means that it improves more than one of the above abilities/skills.