SPOON_OF_GROBO:
Im not sure exactly what you liked about Castor, but just by judging by the Bridge and Tunnel sound, all that I could think to do was give a few options based on guitar interplay, singing style, rockness...Shiner - Starless, Giants Chair - Purity and Control, and Boys Life on the rock side of things. C-Clamp - Longer Waves, and Sharks Keep Moving - Self Titled, based on melodics. Then Braid - Frame and Canvas, maybe even Mock Orange, because I think they're similar to Bridge and Tunnel.
Of course there's also bands like American Football, Colossal, Very Secretary...I could really go on talking about midwestern emo...but to have a bit of restraint here are three albums (most of the others that I mentioned you can find in the thread)
Im fairly sure that you already have American Football and Braid, etc...here's something that's been buried in the "crates" of the genre:
C-Clamp - Longer Waves (Ohio Gold - 1995), because they have a similar sound...and incase its intricate guitar rock that youre after, go for these: Shiner - Starless (O&O - 2000), who's frontman recorded the second Castor album. Then there's the classic: Giants Chair - Purity and Control (Caulfield Records - 1996)
http://www.mediaf!re.com/?ktwtgjmwhgz
http://www.mediafire.com/?otoa5n1iyny
http://www.mediafire.com/?mfninjzjlyy
ENJOY!