I bought the Tamrac system 3 model 5603 camera bag for my S2. It's mid to large in size, but it has many good features. It's tough, it had a weatherproof outer shell, it has good foam isulation that keeps it safe from too much direct sun, as well as drops of a couple of feet. The various pockets are well laid out, and the interior can be confugured to suit almost any setup you desire in a few minutes. It cost around fifty bucks as I recall.
Here is what it keeps ready on hand for me. The S2 with the lens adapter, a UV filter, and the lens hood sit in the upper level, and is well protected. The high power flash fits in a pocket next to the lens.The tele converter with it's own adaper, as well as the wide angle converter and it's adapter sit in their own foam lined pockets, and are ready for use. An S400 lives in a lower compartment. A multi card reader and USB cable live in the front zip flap pockets with the battery charger for the S400. USB and video cables for both cameras are located in the front zip compartment flap pocket. A slide out stiff pocket carries a spare battery for the S400, 8 charged AA batteries for the S2, and a spare gig of memory for each camera. A set of often used 58 mm filters, and a homeade 72 mm polorizer adapter for the Tele converter fit in the lower level of the main case. The top cover has an inside pocket that holds the user manual, a pad, a pencil, a white/grey card, tape, and other needed stuff.
The zippers are strong, the strap rings are stout steel, and there are three strong plastic clips and some Velcro to backup the zippers. I'm pleased with the case, and can attest to the fact that if you are caught in a lengthy downpour, the contents of the case will stay dry. It's not a small case, but it suits the size of the S2, as you can keep the entire compliment of accessories in it without it being too heavy, or too bulky to carry all day long.
I'm sure other brands are just as good, and will have worthwhile features. Still, this bag is as sturdy and well designed as any other I have used over the past 35 years of toting cameras.