Synergies

Strength build
19 synergies: Strength, Constitution, Armor, Construction, Intimidation, Combat, Smithing, Strategy, Dungeoneering

Agility build
17 synergies: Agility, Charisma, Evasion, Hunting, Tracking, Stealth, Artistry, Leadership, Espionage

Intelligence build
18 synergies: Intelligence, Luck, Awareness, Cooking, Diplomacy, Magic, Alchemy, Strategy or Sorcery, Enchanting

Note: The spreadsheet recommends Strategy, which synergizes Luck, Awareness, and Diplomacy. Sorcery synergizes Intelligence, Magic, and Enchanting. This needs testing to determine which is better.

Table of Synergies
Spreadsheet available at Google Documents.