Digital SLR Guide has three articles that give some good background, and make some quite worthwhile recommendations on three subjects that are quite close to the hearts of many digital photographers.

Batteries
Memory Cards
Camera Cases

My opinions on the very same subjects below:

Batteries, I tend to stick religiously to the camera manufacturer's brand. Too much can go wrong there, and if the battery fails in some spectacular sort of way, then it's likely to take out expensive camera innards as it goes. If that happens, say goodbye to your warranty.

Memory cards, I like more, smaller cards rather than fewer, larger cards. My main camera bag has 4 x 1 gig cards in it, my small case has 1 x 512 meg card, and the camera has 1 x 1 gig in it. If I get a failure on a full card, at worst I've lost somewhere around 180 photos. If I used 4 gig cards, I'd have lost around 700. Changing a car takes under a minute, and you don't have to fill cards completely. I tend to start looking for a spare moment to change cards when I hit around 20 shots left on the card. The other benefit of buying this way, is that the smaller cards are cheaper per gig at the moment, so I can get more storage for fewer dollars.

I have two main camera cases for my digital gear - my main 'take out' case, which has space for spare batteries for both the camera and the flash, the main flash unit, the camera body with standard lens attached, a 100-300mm zoom, a couple of boxes of filters, some various sundries like a notebook and pen, a few business cards, some cleaning cloths, and a couple of ziplock plastic bags. My 'I'm in a hurry' case just fits the camera body and standard lens, with an external pocket for a spare 512 meg memory card.