Just FYI--because someone mentioned it above.....Shedd Aquarium's Onceanarium is closed for remodeling. We were planning a last minute weekend getaway for this weekend. Glad I checked their website first.
I haven't been there in a while, but Sea Escapes in South Elgin was good when i was in there. http://seaescapesltd.com/ Don't recall angels, but a very nice shop.
a few minutes south of there is Critters, and while its not a big store, they did have some interesting freshwater fish there in the past (like shell dwellers), including some very nice adult angels. Once again been a while since I was there. http://www.critterspetshopinc.com/
if you are heading home on I-80, creepy crawly critters in Ottawa IL is worth a stop. once again a small shop, but what the do have tends to be good and they stock some rarer stuff (exotic pleco's, cichlids, I have seen some nice angels there).
If your not familier with the quad cities area, theres some places there worth checking out as well on the way home.