I also just bought my S2 IS and went shopping for a new bag. I was not able to find the Lowepro models mentioned above, but I did find what I think is the perfect bag for this camera. It is the Quantaray QC-BN ($20) which I bought at a Ritz Camera store in our local mall. I don't believe a bag could be a better fit if it had been designed specifically for the S2. There is a zippered pocket on the front that is just right for 4 spare AA's and a smaller zippered pocket inside the flap of the larger pocket that is perfect for a couple spare SD cards. I'm not sure how available this bag is if you don't have a Ritz store handy. I checked on their website to see if it is listed there and it is the very last bag listed if you do a search using Quantaray bags. It does not list it as a QC BN, but the store ID stock #, 441662491, is the same as on the card that was on the bag.
This is for the camera out of the box and not with any adapters, filters, etc.