I have been to great weddings at the Historical Society, Garfield Park Conservatory, Promontory Point, and several of the chapels on the University of Chicago campus. I'm told all were quite reasonable as weddings go.

IIT's Chapel,
plenty of space outside for the party and band

I've heard goods things about the banquet room at the top of Hotel 71. Also, supposedly you can get married at the Cultural Center...? If so, that would be gorgeous. The Botanical Garden is probably the most beautiful choice, but I'd bet it's booked like years in advance.

Thanks for all the suggestions - greatly appreciated. Any more are welcome!

Tree Studios...

We're especially looking for some venues with architectural significance, so I really appreciate some of these suggestions. Definitely a few that I wouldn't have thought of.

A New Leaf is a cool venue, it is connected to a floral shop. It has a unique indoor space as well as a courtyard in the back. They have a lot of weddings there, if you walk by on a Saturday night you can usually see one in progress.

http://www.anewleafchicago.com/event.php

Wow - New Leaf looks awesome. Thanks for the heads up.

We got married at Promontory Point. Outside ceremony with reception inside the field house. Very beautiful space and it fit into our budget. Loved it because we didn't have to do much to the space.

Here are some other unique spots:

http://www.westloopstudio.com/
http://atriumeventschicago.com/
http://www.gallery-1028.com/
http://www.prairieproduction.net/

i'm sure it's not cheap, but you can have a wedding at spertus

I just looked into Spertus, and it's actually relatively reasonable. Cool.

new leaf is great but often booked up. just a heads up. spertus is cheap but I think you have to use their caterer (?)

I know the Cultural Center meeting room reservations are ridiculously cheap. Not sure about banquet-size facilities though. Also they have a secondary space which is a smaller arts studio called... studio 37 or something like that.

For arch significance, you might look into whether Garofalo's Hyde Park Arts Center allows weddings.

My wife & I lived in Chicago & she worked as a florist doing weddings. She says Cafe Brauer, in Lincoln Park by the zoo is the BEST place for a wedding/reception! "It's the prettiest place we ever did a wedding!", she said.
Best of luck!

wooden gallery on wolcott. there are many studio/loft spaces for rent in west river. it's worth asking around.

came across this trying to remember the name above:

http://www.stefanicatering.com/venues.html

that reminds me - there's that awesome vintage antiques place that does weddings. That's where I would have a wedding, maybe. What the heck is the name of that place... restoration? something like that?

yes that's it!

i've been to a party at salvage one - it's a great place!

There is also Architectural Artifacts in Ravenswood - which has a great atrium space. No idea if they do events though.

http://www.architecturalartifacts.com/

edit - yes they do.
http://atriumeventschicago.com/