Where can I find a graph of the estimated size of each mining pool relative to the overall hashrate of the entire bitcoin network?
The http://bitcoinwatch.com/ site gives a pie-chart of the hasrate distribution by mining pool.
Hashrate distribution An estimation of hashrate distribution amongst the largest mining pools
Time for an update! At the moment, the following sites feature charts about the distribution of mining pools:
- Bitcoinity (hash rate)
- Blockchain.info (number of blocks mined)
- Blocktrail (number of blocks mined)
- Coin Dance (number of blocks mined, including support for proposals)
Disclaimer: I didn't check the accuracy of the data, and a pool's hash rate will vary over time. The number of blocks mined will vary randomly, of course.