I finally found a fix for the glitch where Brynjolf is stuck in the market and won't go down to the Ragged Flagon.
This will take some patience. You'll need to sprint into Brynjolf so you push him. Push him all the way down to the Ratway door. Now talk to him and exit the "speak menu" quick and enter the Ratway before he get to finish his line. You'll now see him in the Ratway. Now attack him and take him to the Ragged Flagon. He will follow you inside. Run to the other people in there and yield. Speak with Brynjolf. Complete the task he gave you and talk to him in the market where he's still glitched. He'll give you a new quest. Follow him, complete the quest and the glitch is gone.
I suggest that you save now and then.
I haven't found any other fix for this yet. Hope this helps someone.
I'm on the 360, by the way so....HUZZAH!!!! You're a genius!!!!
Spread the word!!! A LOT of people have had this problem. You should google it as if you were looking for a way to fix it, then reply to one or two of the results. I'm sure the fix will spread like wildfire.