Jamie stated in another thread:

Whisky is very nice indeed, but it plays second fiddle in my book to a wonderful gin cocktail
I summertime, I find myself gravitating toward gin-based cocktails too. It really is a very versatile spirit and lends itself well to a multitude of different moods.

I don't know what style of cocktail you like, but I figured I'd share these recipes with you. I put asterisks next to the ones that are my favorite, although they're all good (except the Plantation - I found it disgusting but it came highly recommended so I'll pass it on).

Ramos Gin Fizz*:
Created in 1888 by Henry Ramos at the Imperial Cabinet Bar in New Orleans.
1.5 oz Gin
0.5 oz fresh lemon juice
0.5 oz fresh lime juice
1.5 oz simple syrup
1.5 oz heavy cream (you can use half-and-half as well, but it won’t be as rich)
1 small egg white
2 drops (no more) of Orange Flower Water
Soda
Secret ingredient – 2 drops of vanilla extract
Shake all ingredients with ice except the soda for a really long time. Count the seconds until your arm really hurts from shaking, and then count the same amount backwards. The trick to this drink is to make it as silky-smooth as possible (where it won’t separate in the glass). It helps to dry shake the egg white before adding the other ingredients. Don’t add too much soda at the end (I sometimes skip it entirely, if the drink seems too watery already). This is a great drink for weekend mornings as well as in the evenings.

Earl Grey MarTEAni:
(from the Pegu Club in Manhattan)
1.5 oz Earl-Grey gin infusion
0.75 oz fresh lemon juice
1 oz simple syrup
1 egg white
1 lemon twist, for garnish
Lemon Zest sugar, for garnish
Shake first four ingredients in a Boston Shaker with ice, strain into a chilled cocktail glass rimmed with the lemon zest sugar.

Earl Grey Gin infusion:
¼ cup loose Earl Grey tea leaves
1 liter Tanqueray gin (or whatever brand you want)
Add tea leaves, recap, and shake well. Allow to steep for 2 hours, strain gently. DO NOT press the tea leaves to extract the excess gin – this will make the infusion bitter.
Obviously, you can scale it down for a few drinks.

Lemon Zest sugar:
1 lemon
½ cup granulated sugar
Finely grate the zest of the whole lemon, being careful not to include any of the white pith. Add sugar and mix well. Keeps at least a week in the refrigerator.

Cucumber Smash*:
(recipe is for 2 drinks)
4 oz gin
3.25 oz lime juice
1.25 oz simple syrup (more, if desired)
~25 thin slices of cucumber – use an English cucumber if available (they’re longer, thinner, and have slight ridges down their length).
Muddle the cucumber, lime juice, and simple syrup. Add gin and shake w/ice in a Boston Shaker. Strain into old-fashioned glasses or highballs with fresh ice.

Corpse Reviver #2*:
It has been around since the mid-1800’s, but this version is from New Orleans. Harry Craddock’s “The Savoy Cocktail Book” from 1930 noted, “four of these taken in swift succession will unrevive the corpse again”. The drink was originally intended “to be taken before 11am, or when steam and energy are needed”. Darn good drink…and easy to remember.
0.75 oz gin
0.75 oz Cointreau
0.75 oz Lillet Blanc (you can find this at better liquor stores, it’s a French aperitif)
0.75 oz lemon juice
A few drops of absinthe substitute or pastis
Shake with ice, strain into a chilled cocktail glass. Garnish with a maraschino cherry.

The Plantation:
4 to 6 fresh basil leaves
½ tsp sugar
1 oz gin
½ oz Cointreau
½ oz fresh lime juice
1 oz fresh grapefruit juice
¼ slice grapefruit for garnish
Muddle the basil and sugar in the bottom of a mixing glass (Boston Shaker) to make a paste. It should look like pesto. (You don’t need to add any liquid here because there is water in the basil leaves.) Fill the glass with ice. Add the gin, Cointreau, lime juice, and grapefruit juice. Cover, shake until cold, and strain into a chilled cocktail glass, preferably through a fine-mesh sieve. Garnish with the slice of grapefruit.
NOTE: Add a bit of soda water and pour it over ice to turn this drink into a refreshing summer cooler.

Aviation (1916):
2 oz gin
0.75 oz Maraschino liqueur
0.5 oz lemon juice

Pegu Club Cocktail (1930):
2 oz gin
1 oz triple sec
0.5 oz lime juice
Dash Angostura bitters
And/or orange bitters

White Lady:
1 oz Cointreau
2 oz gin
½ oz lemon juice
Shake and strain into a chilled martini glass.

Negroni:
1 oz Campari
1 oz Italian (sweet) Vermouth
1 oz gin
Orange Peel, for garnish
STIR and strain (don’t shake – this is a French-style drink), and squeeze the orange oils across the top.

Old Flame:
1 oz gin
½ oz Italian Vermouth
½ oz Cointreau
¼ oz Campari
1 ½ oz orange juice (fresh-squeezed)
Orange Peel
Shake and strain, then FLAME the orange peel.
To flame the peel, hold a lit match over the drink, and squeeze the rind so that the oils ignite as they spray across the drink. Takes a little effort to get it right, but it makes a really neat flavor.

Jasmine:
2 oz gin
1 oz Grand Marnier
½ oz Campari
¾ oz lemon juice
Shake/strain.

Singapore Sling*:
2 oz gin
3/4 oz Cherry Heering
2 tsp Benedictine
2 oz pineapple juice
3/4 oz lime juice
2 dashes grenadine
1 dash Angostura bitters
Soda water
3 brandied cherries
Shake/strain (without soda water) into ice-filled collins glass. Top with soda & garnish.

Bijou (also called the 'Jewel' if you use equal parts for all ingredients):
3 parts Gin
1 part Italian Vermouth
1 part Green Chartreuse
Shake (even though this is a French-style cocktail) and strain. This drink needs some abuse.

The Last Word:
equal parts:
Plymouth Gin
Maraschino Liqueur
Green Chartreuse
Lime Juice
This is a little on the chest-hair side. Best as the last drink of the night when you're blitzed.

Colbert Bump:
1.0 oz cherry heering
1.5 oz gin
0.5 oz lemon
soda water
Stirred in a highball with ice.

The Bramble:
2 oz gin
1 oz lemon juice
1 oz simple syrup
¼ oz Crème de Mure (blackberry liqueur – you could use Chambord in a pinch).
Stir & top off with soda.

The Blue Moon:
(from Crosby Gaige’s Cocktail Guide and Ladies’ Companion, 1941)
2 oz gin
0.5 oz Crème de Violette
0.5 oz lemon juice
Shake and strain.

The Monkey Gland:
(from Harry’s New York Bar, Paris, 1920’s)
1.5 oz gin
1.5 oz orange juice
1 teaspoon grenadine
1 teaspoon absinthe or pastis (Pernod or Herbsaint will work as well)
Shake and strain.

French 75*:
(named after a WWI field artillery piece – it can pack a punch!)
2 oz London dry gin
1 tsp superfine sugar (powdered sugar)
1/2 oz lemon juice
5 oz Brut champagne
Shake the first three ingredients hard with ice and pour into a chilled glass. Top off with champagne and lightly stir.