We did "flames" (or flamers) after meetings. Chapter members would put notes in a basket and the basket would be passed around and everyone would take one (or two depending how many were left) and read them out loud. They would say congrats on your A in accounting or I'm glad we got to spend time together or You are the greatest little in the world! ... stuff like that.
My chapter also had pockets. They were basically sewn onto a quilt (by a loving alum) and each member decorated a wooden heart pin on the outside. People left keys and phone messages in them, but we also had times where we left notes for each other.
Another option is to have an ongoing competition. You can great the chapter into small groups/teams and have small activities they need to do to earn points. Ex) Take a picture of your entire team on campus in letters; Do something nice for another sister and leave your team's name but not who exactly did it; Deliver flowers/cookies/cards etc. to another sorority chapter as a team; Do some sort of community service together ... you get the idea. New ideas can be sent to the chapter weekly and they can have a point value. The team with the highest points win some sort of prize. Afterwards during an informal chapter meeting and ask people to share their favorite moments as a team and to point out things other teams did that were creative or really nice.
My chapter LOVED LOVED LOVED our yearly game of assassin (a little too much love actually). Everyone had a $0.50 squirt gun and was given a name, once they "assassinated" their member they took that members name. (Logistically the names must be put in a circle member A has B, B has C, C has D, D has E and E has A) Every day there was another way not to get caught. You can't be caught on monday if you are in letters, tuesday if you have a stuffed animal with you, wendesday if you are wearing a tie, stuff like that. You can also pick safe place though our only safe place was in the shower
I know this is long but my last suggestion is a game of pass it on. You find one (or a couple) important objects, say a decorated pillow. Let everyone know that when you have the pillow you are asked to do one nice thing for a chapter member; ask them to get coffee with you and chat, bring them a snack when they are studying, leave them a note saying how much you appreciate them, then you pass the pillow to them asking them to do something for someone else.
I hope these were a little helpful. Jump in everyone else ... I've heard tons of great ideas from you all before!
Edit:
Although I agree wtih the RESPECT program and think its great (and encourage you to look there), there are also other places to seek advice.
There are a ton of ideas at the end of the VPNME handbook (and other handbooks too ... its just the one that I can remember exactly whats in it).