My favorite Hi Ball of all Time is Vernor's(an obscure, potent ginger all type soda) and whiskey. Two powerful flavors that manage to keep their potency while still blending very well.
As a general rule for all of these Using a 12oz glass, I would pour 1.5 oz of liquor with 4.5oz soda directly over ice- stir gently. Drink with a full sized straw. Garnish with lime, orange, cherry, or lemon as appropriate. (The straw may seem unimportant, but in fact it creates a different experience than a sip straw or no straw)
If you're into sweet things I recommend Tuaca and Cream Soda (Jones' is my favorite for this). Tuaca is 80 proof and is sort of a Vanilla and Orange Liquor with butterscotch after notes. It's sweetness blends well into soda(also Vernor's as above, coke, orange soda, etc..) and very efficiently hides the alcohol.
Some traditional Hi-Balls:
Vodka with Soda Water and Lime: Descriptive words: Strong, simple, skinny, diet, crisp
Spiced Rum and Coke- Quite different from a cuba libre. Descriptive words: Sweet, easy, deceptive, spiced, flavorful
Vodka and Tonic and Lime: Descriptive words: Strong, simple, skinny, diet, potent, blunt, Quinine
Jack Daniels and Ginger: Descriptive words: Sweet, Bright, Easy, Traditional
Scotch and Soda (The original Hi-Ball): Descriptive words: Traditional, potent, slow-sipping
Some non-traditional quick combos:
Cake Vodka and Coke: Descriptive words: Soda Shop, Sweet, Vanilla Coke, Rich
Whipped Cream Vodka and Orange Soda: Descriptive words: dessert, old-fashioned, soda shop, masked alcohol, deceptively strong
Pear or Apple Vodka and Sparkling Apple Juice: Descriptive words: Apple Pie, Crisp, Sweet, Refreshing
Skinny Bitch - Vodka and Diet Coke: Descriptive words: Diet, skinny, easy
Dirty Shirley - Vodka (or cherry vodka) Ginger Ale (or Sprite) and grenadine(3/4 oz): Descriptive words: Sweet, fun, masked alcohol, deceptively strong, bubbly
Double O-7 - Orange Vodka/ lemon vodka orange slice or splash of OJ mixed with 7/up sprite : Descriptive words: Crisp, lively, effervescent, citrus, refreshing, bubbly
Swamp Juice (Named for color of beverage) - Mountain Dew and Captain Spiced Rum: Descriptive words: Energizing, sharp, citrus