Here are the latest low prices at Amazon.com for Compactflash, the Sandisk 512mb and Viking 256mb are particularly good prices:
Sandisk 512mb: $63.99 (after $20 rebate)
Sandisk 256mb: $41.99
Sandisk 1GB: $166.99
Viking 512mb: $85.99 (after $25 rebate)
Viking 256mb: $35.99 (after $15 rebate)
Viking 1GB: $165.99 (after $45 rebate)
All come with free shipping.