Mar 062013
 

Note: While this chart is good for showing what hops are typically related in style, each hop is unique, and therefor this chart will only steer you in the direction of general substitutions and not exact clones.  For example, substituting Amarillo Gold for Cascade or Centennial will give you vastly different beers in terms of flavour and aroma, but will give you a beer that tends to fall under the same catagory (i.e. West Coast Pale Ale).

Hop Variety Substitute Varieties
Admiral Target, Northdown, Challenger
Ahtanum Amarillo, Centennial, Cascade
Amarillo Gold Cascade, Centennial
Bramling Cross EK Goldings, Progress
Brewer’s Gold Chinook, Galena, Nugget
Cascade Amarillo, Centennial, Columbus
Centennial Amarillo, Cascade, Columbus
Challenger Perle, Admiral
Chinook Brewers Gold, Columbus, Nugget, Northern Brewer, Target
Cluster Galena
Columbus (Tomahawk) Chinook, Northern Brewer, Warrior
Crystal Mt. Hood, Liberty, Hallertauer, Tettnanger
First Gold East Kent Goldings
Fuggles Willamette, Styrian Golding, Tettnanger
Galena Chinook, Nugget, Pride of Ringwood
Goldings, East Kent Progress, WGV
Green Bullet Styrian Goldings
Hallertauer Hersbrucker Mt. Hood
Hallertauer Mittelfrueh Liberty, Other German Hallertauer
Hallertauer, New Zealand Perle
Horizon Magnum, Warrior
Liberty Hallertau, Tettnanger, Mt. Hood
Magnum Nugget, Galena
Mt. Hood Hallertauer, Liberty, Crystal
Northdown Admiral, Challenger
Northern Brewer Chinook
Nugget Cluster, Galena, Brewers Gold, Target
Pacific Gem Magnum
Perle Challenger, Northern Brewer
Phoenix Challenger, EK Golding
Pilgrim Pioneer, Target
Pioneer EK Golding
Pride of Ringwood Cluster, Galena, Brewers Gold
Progress Fuggles, E.K. Goldings
Saaz Very difficult to substitute, maybe Tettnanger
Santiam Tettnanger, Spalt, Hallertau
Spalt Santiam, Tettnanger, Hallertau
Simcoe Northern Brewer Maybe
Sterling Saaz
Styrian Goldings Fuggle, Willamette
Target Nugget, Fuggle, WIllamette, Admiral
Tettnanger Hallertau, Liberty, Fuggle, Spalt
Vanguard Saaz, Hallertauer
Warrior Saaz, Hallertauer
Willamette Styrian Golding, Target, Fuggle, Tettnanger

Source: http://www.mashspargeboil.com/common-substitute-hops/