Magnum is a great bittering hop with an aroma similar to a strong Willamette. It therefore works well with Willamette, Fuggles, and British Kent Goldings when used as an aroma hop in later boil additions.  Magnum makes an incredibly useful bittering agent in just about any beer, and due its very smooth bitterness, you can really use as much as you want. For example, we use two full ounces in our 60 minute IPA boil. It has a great storage stability too, so stock up! 
 
Substitutions: Nugget, Columbus, Horizon