I remember reading before that Alchemy was a house blend of a few different varieties. I really like the 07 pale, very tasty. Good in the bottle, much better on draft.
Widmer's page says:
BITTERNESS
34 IBU
ALCOHOL BY VOLUME
5.4%
ORIGINAL GRAVITY
13.25° PLATO
MALTS
Pale, CaraVienne 20-L, Caramel 80-L, Carapils
BITTERING: Alchemy
AROMA: Alchemy, Summit
DRY HOPPED: Summit, Chinook
So if what I've heard is true about Alchemy being a blend of different hops, it wouldn't include Summit or Chinook. So I'd guess probably something like Cascade, Centennial, and something else. I'm sure if you can hit the IBUs with some pacific northwest hops it'll be pretty close.
Edit: I looked at some other widmer beers that say they include Alchemy. The 06 Hoppy Red Ale had Alchemy, Simcoe, Cascade. Okto has Alchemy, Mt Hood, and Tettnanger. Snowplow has Alchemy and Willamette. Broken Halo has Alchemy, Cascade, Zeus. Drop top has Alchemy and Simcoe. Hefe has Alchemy, Willamette, and Cascade. So I'd suspect Alchemy is just some reasonably high AA% bittering hop that isn't included in the previous list, maybe centennial, columbus, magnum, galena, and/or warrior. Just a guess.
Another edit: I was googling a bit and found a page on another forum where someone claims "I use a blend of Magnum/Warrior/Horizon in alot of my beers as the bittering component. It's the blend that Widmer uses (they call it their Alchemy blend). " So that seems to jive with what I would think.