I too have an S230, as well as a Nikon Coolpix 4500.
When I first got into digital photog way back when (1998?) I bought a lexar 256MB CF card. Lexar cards are very, very good. Kind-a pricey though.
If you want to spend the $$ I cant recommend a better card.
http://www.digitalfilm.com
More recently though, with the 2 cameras I needed another card, and more space. Viking had a rebate offer on CF cards a few months ago, so I picked up 2 512MB cards for about $100 each after rebate. Not quite as fast as the Lexar card, but very comparable. I like them, and would buy them again.
Heres a link to the 512 still with the $50 rebate on buy.com.
And heres the 256. Only a $20 rebate though.
I'd go for the bigger size. You'll outgrow the 256 pretty quick. At least I did.
For awhile I had a 1GB IBM microdrive, but it was too slow. Camera start up time and read and write times, I found to be unnacceptable, so I ebayed it, and picked up the 2 vikings.
You can also look
here for a pretty good comparison of CF cards and their speeds. Its a lot of info to get through, but its really useful.
Depending on what card you get you'll also want to get a USB card reader. The Lexar cards come with one, but for the Viking youll have to pick one up seperately. I dont know about you but I found that the Canon software really stinks. I just pop the card into the card reader, and it appears as a new removable hard drive on my PC. I can then just drag and drop, no sweat.
Heres a bunch.
On a seperate note, if youre a swimmer, diver or snorkeler pick up one of
these for your Canon.
I got one for a sailing trip to Hawaii I did this winter. Its great! In fact my avatar was taken with it.
Even if you dont swim its great for just protecting the camera when you go to the beach or out in the rain.
Actually,
J and R has it $20 cheaper.
Good Luck!