Your mortgage rate can make a big difference to the money coming out of your pocket.  If you put in a little legwork to get the best mortgage rate now, it could save you thousands of dollars down the road.

But what "best" means will depend on a lot of individual factors, including your credit score and the length of time you stay in the house.  Here are some suggestions for finding the best mortgage rate for your situation.

What a difference a rate makes
Say you have a $250,000 loan over 30 years.  At a 7.5% interest rate, your monthly payment on the mortgage is nearly $1,750.  At 6%, it drops to $1,500, and at 5%, you only pay $1,350.  Back in 1981, you could have reasonably expected to get a mortgage with a 14.5% interest rate -- so your payment on that same loan would have been more than $3,000 a month.

You can calculate how different rates affect your monthly payments at of a number of mortgage calculators online.  Two good sites for a variety of online calculators are HSH Associates and The Mortgage Professor.

What you can't control
With a mortgage rate, there are factors you can't control and factors you can.  You can't control how the Federal Reserve is setting interest rates; the Fed's published rate influences the rates at which banks can lend to each other.  If you happen to be taking out a loan at a time when interest rates are high nationally, all the good behavior on your part isn't going to get you a loan at 4% interest.

You also can't control how the lending companies evaluate your credit report.  But you can take a few steps to make your credit report look better before you start applying for loans, such as getting free copies to check for errors, paying off existing debt (to lower your debt-to-income ratio), and not opening new cards or taking on major new debt, such as a car loan.

Shop around
What you can control is who you get the loan from.  You can go through a broker, who will look for the best loan rate for you, or shop around on loan providers' sites yourself.  You want to make sure you're comparing apples to apples: get several quotes in one day, rather than over the course of a week or month, as rates may change. (You also want to do your comparisons relatively quickly because it will minimize the number of times inquiries show up on your credit report.)  Once you settle on a loan, you want to find out how long that rate can be "locked in".  Make sure to compare the annual percentage rate, which includes other costs you'll be paying, and not just the quoted interest rate.

Down payments and points
There are two other major factors under your control: the size of your down payment and "points."  In general, the larger the down payment, the smaller the interest rate over the life of the loan will be. 
Points, meanwhile, are an upfront cost.  A lender might offer you a loan at 6.25% and 1.25 points or 5.5% at 3 points; the higher the rate, the fewer the points.  Generally you pay one percent of the loan per point; so you essentially choose whether or not to pay more money up front to get the lower interest rate.

With both the down payment and points, the question you have to ask yourself is how long you see yourself owning the house.  If you only plan to hold the loan a few years, it might not be worth it to pay a lot of cash up front to reduce the loan over time.  But if you plan for this house to be a long-term investment, you'll save money over the years by paying points to get the lower rate.