http://www.mymoneyblog.com/archives/2006/10/the-ultimate-interest-rate-chaser-calculator.html
I wish I'd seen and used this calculator before moving my money from Citi's MM saving to HSBC's MM savings to take advantage of their 6% promotion.
Frankly, the difference isn't it worth it to me. But, it's too late now. On January 31st, I moved my savings into HSBC where it stays until April 30th. After that, I may leave it in HSBC or move it back to Citi and lose three days interest and thus come out ahead by very, very little. So much for rate chasing for me!