Sources of money to use for your down payment when buying your home.

[edit] Steps

Determine approximately how much money you need. Your banker or mortgage broker can help you with this. Your real estate agent should be able to help you if you haven't gone to the lender yet.
Investigate local bank programs. Sometimes lenders will provide mortgage loans, particularly to first time home buyers, that require NO down payment. There are federally guaranteed loans that are often available through the VA or the USDA. These require no down payment - which is just as good as getting a grant, eh? Federal programs from the FHA insure loans so local lenders will make minimal-down payment mortgage loans.
Look into HUD (Dept of Housing and Urban Development - a huge Cabinet agency, 2nd in size only to the Dept of Defense). This department has a very under-used, but super program that grants money for down payments. This program is called: ADDI, or American Dream Downpayment Initiative. A clickable link to it is on my website (that URL is below) or just search for HUD.
Consider private "charitable" sources of downpayment money. Most of these essentially require the seller to fund your down payment. This is rarely a good idea. You have (hopefully) wrung enough other concessions out of the seller, like a very reduced price, that s/he will refuse to do this for you. But - no matter, you can almost certainly do this on your own.
Remember to be patient. After all, you will be dealing with civil servants! (Civil servants are quite often dedicated public servants that stand up for the public's long term best interest (as opposed to politicians who sometimes stand for their own short-term ephemeral interest). That said, they are often underpaid and overworked, and have built stable systems in an ever-volatile democratic government. Therefore, they sometimes appear ornery and difficult. Keep in mind though, there may be a method to their madness.