I figured we should start a reference thread with a list 27" tire options since it seems like this question comes up every other week or so. If you have any additions, changes, or notes, add them and I can update this first post.
Good Tires:
Panaracer Pasela Protite - Folding bead
Folding / Gumwall - 27" x 1 1/4" (350g), 27" x 1 1/8" (270g), 27" x 1" (250g)
Panaracer Pasela Protite - Wire bead
Wire / Gumwall - 27" x 1 1/4" (410g), 27" x 1 1/8" (330g), 27" x 1" (310g)
Panaracer Pasela
Gumwall - 27" x 1 1/4" (360g), 27" x 1 1/8" (300g), 27" x 1" (290g)
SwiftTire Sand Canyon - Black / 66 TPI
Black Sidewalls - 27' x 1 3/8" (350g)
SwiftTire Sand Canyon - Tan / 66 TPI
Tan Sidewalls - 27' x 1 3/8" (350g)
Schwalbe Marathon HS
Blackwall - 27" x 1 1/4" (660g)
Schwalbe HS159
Off-white sidewall - 27" x 1 1/4" (550g)
Continental Gatorskin
Blackwall - 27" x 1 1/4" (330g)
Continental Ultra Sport
Blackwall - 27" x 1 1/4" (380g), 27" x 1 1/8" (370g)
Vittoria Zaffiro IV
Blackwall - 27" x 1 1/4" (480g), 27" x 1 1/8" (390g)
Origin8 Elimin-8er
Black, white, red, or blue - 27" x 1 1/4"
Michelin Protek
Gumwall - 27" x 1 1/4" (650g)
Bontrager T1
Blackwall - 27" x 1 1/4" (440g)
Cheaper tires:
Bell (Walmart) Sports 27" Tire
Blackwall - 27" x 1 1/4"
Kenda K35 Street Tire
Gumwall, skinwall, or blackwall - 27" x 1 1/4" (500g)
Cheng Shin CST C740 / Nashbar Prima 2 Plus
Blackwall - 27" x 1 1/4" (280g)
CST C740 Also available in all White and all Red
Sunlite version available in whitewall
Wider / cross tires:
Kenda K161 Krosscyclo
Gumwall (knobby) - 27" x 1 3/8" (401g)
Sunlite Hybrid V-Track tires (rebranded Kenda K161)
Gumwall (knobby) - 27" x 1 3/8" (401g)
Kenda K40 Street Tire
Gumwall - 27" x 1 3/8" (470g)
Retailers / Where to buy:
Try your local bike shop first to see what they have in stock. If you want to order online, here are a few options: