Fun & trendy lunch spot, still a bit casual
Where, downtown? "Downtown" covers quite a wide area, from the Gold Coast and Mag Mile down to the South Loop.
Depending on which downtown neighborhood you'll be heading to, I recommend the following places for a fun, trendy, casual lunch...
Frontera Grill/Topolobampo (Mexican) - www.rickbayless.com/restaurants
Nacional 27 (Latin fusion) - www.nacional27.net
Cafe Iberico (tapas) - www.cafeiberico.com
Quartino (Italian "small plates") - www.quartinochicago.com
Bin 36 (wine bar) - www.bin36.com
Incidentally, French bistros are not at all stuffy - quite the contrary! The whole idea behind French bistros (and any other kind of bistros), as opposed to fancier, more formal restaurants, is that they are supposed to be casual, moderately-priced, friendly neighborhood-type places. Just to cite one of our best as an example, I've never heard anyone refer to La Sardine ( www.lasardine.com ), in the West Loop, as "stuffy", LOL!