I was recently trying to decide whether or not it was financially advisable to refinance my 2 year old mortgage. I found a great site full of mortgage related calculators and advice that I wanted to share with the community.http://www.decisionaide.com/MPCalculators/menus/MP_Calculators.asp
I am still trying to make up my mind because refinancing will drive up my PMI costs enough that I won't really be saving money until about 3 years from now - and of course the interest is tax-deductable but PMI is not. However, it is unlikely that we will sell our house, so we will most likely save a great deal of money by the end of the mortgage by refinancing at current rates.
But the site has great info for comparing loans, refinancing offers, payoff things (including tax implications) and even prepayment plans that fully display the amortization tables.