I have not read the other responses, and I'm sure I'll get flack for this...stop picking her up and leave the room! That is why she continues to cry - because you have now chained a behavior - you have to break the chain. Cry = emotional mom standing right there with her = pick up baby. It's a conditioned response, just as when someone sneezes, we say "God bless you".
I don't know what has worked for others, but I can tell you my experience with my child. At 6 months old we faced all of the same problems. She would cry anytime you put her down, so we basically had to rock her to sleep. Once she was asleep, we would put her down in the crib but she would wake up screaming 10 minutes later.
We started the "Ferber method" (I hear the sighs already),a nd it WORKED! Not only did it work, but we only had to do it for TWO DAYS. By the third night, she fell asleep in less than 10 minutes and has never had a problem since!
The Ferber method is all about having the SAME ritual every single night. Take a bath, dry off, get dressed, brush teeth, and putting the baby to bed. Maybe you want to rock for a few minutes, or maybe cuddle for five or ten minutes first. Once you walk into her room, put her down, say good night, tell her you love her, pat her back or tummy, then leave the room.
Set a timer - wait 10 miuntes, even through her blood curdling screams, then go in, pat her tummy or back for one minute, DO NOT TALK, then leave the room again. Now set the timer for 15 minutes. Do this over and over, adding 5 minutes to the timer until she falls asleep. Have a bottle of wine ready the first night cuz you'll need it!
The next night, do the same thing. By the second night, my daughter was asleep after my second reappearance (so about 30 minutes). The third night, she stopped crying and went to sleep in less than 10 minutes; I never had to go in there!
Now some people I know have had to do this for up to 3 weeks. But the consistency will set in, and she will go to sleep a little earlier each night knowing that you are still there even though you are not in the room with her. Good luck!