Morning, With my K100 I have been using PNY, PQI, Pairtoit, Kingston, Transcend, with no problems. I will not use A-Data, as others have had too many reported problems. I usually get class 6 cards, but with the K100, speed is not really an issue (class 4 or 133x is more than sufficient). I have a number of 1GB, 2GB and 4GB cards. I use the 4GB cards in my K20 and LX3, with the larger image size. I think that the smaller sizes are perfect (at least for me) in that you are going to download them probably the same day. I am now doing large multi-row stitched images (with HDR) so yes I can burn through 100 images for a single shot, and I am going to need to get a larger card.
Several years ago, folks were suggesting the smaller cards were better in the event of a failure, you loose fewer images. I have never had a failure (yet).
I use to order mail order when I found good prices. I have not bought cards for well over a year (a year ago Thanksgiving Scandisk had a free special and I picked up 3).
The current prices for a 1GB card is about $4
sd cards 1gb - Google Product Search
.. with 2GB cards going for $5 to $10
sd cards 1gb - Google Product Search
I would NOT buy SDcards off of evilbay.
Batteries - The best batteries I have ever used bar none are Energizer e2 Photo L91 Camera battery - AA - Li 2900 mAh. They are not rechargable, but they last forever and are cheap.
Energizer e2 Photo L91 Camera battery - AA - Li 2900 mAh
The K100 is a very nice camera. I kept mine and have it in the truck (all the time) with the 2 kit lenses, and its perfect.