Amazon.com has a great deal on high-speed compactflash memory cards at the moment.
You can get for the Lexar Professional 80x 1gb CompactFlash card for $50 (after $30 rebate expires 9/30).
Note: if you see a price higher than $80 then Amazon is sold out and they are defaulting to a seller such as Office Depot or Tigerdirect. Wait for Amazon to have them back in stock at the lower price.
Do you really need a high speed card? well a regular card has a write speed of 600kb a second, but this card has a write speed of 12mb a second. We will have a review in a couple of weeks looking at a number of high speed cards and seeing where they come in useful (hint: if you want to take advantage of the 5 shot per second burst speed on the 8.2 megapixel Canon 20D camera you will need a fast card).