Down-payment assistance is NOT going away. What will be prohibited is a seller promising to make a donation to a DPA provider like Ameridream and Ameridream making a gift to the buyer. This prohibition goes into effect for borrowers who have not been credit-approved for their loan by 9/30/2008.
You will still be able to get real grants and gifts to assist you with your down-payment. Charitable organizations have been making non-contingent gifts for years as well as government agencies.. This will continue plus assistance from your own family as gifts or loans.
The other contributors here have mentioned the new tax credit, but it is not a gift. If you are a first-time buyer, then you can get up to $7500 for a couple as a credit on your next year's Federal taxes. You will have to pay back the credit 1/15 per year over the following 15 years. Yes, it is like an interest free loan, though.
You should always explore other options for financing, besides what a builder may have arranged. Often the builder has structured the deal so that using his recommended lender will save you money. Sometimes the savings are not so obvious, and sometimes they're quite genuine, because the builder has acquired funds at a low rate before starting the development.
The state of Texas has at least two programs right now that you can use for assistance and subsidized interest rates here in Rockwall. Other programs are tied to Dallas city and county or other municipalities. Check with your loan officer.

The mortgage landscape is changing all the time. The general trend though is quailifying is getting more difficult or the standards have been raised. Removing the ameridream type programs is one of those changes. Lenders now want the buyers to have some vested interest in the purchase. I believe FHA still allows the seller to contribute up to 6% of the purchase price towards downpayment or closing costs, but the home has to appraise at a price that allows that and that part is getting trickier too. I always suggest buyers get preapproved with one lender when you are ready to start shopping for a home. Once you get a contract then if you want to compare different lenders you can do that. Remember always take your realtor the very first time you even visit a builder. Based on the unending stream of problems we see on this website, you'll be glad you did.

Downpayment assistance is going away as of Sep 30. There is no word on when or if it may make a return. It has been replaced by a $7500 tax credit, which is really an interest free loan payable over 15 years.

As far as third parties at closing, you will need to pay a certain amount of closing costs related to the transaction with the title company. You can avoid paying these costs if you know someone who is an attorney and can draw up all of the paperwork for you pro bono. Otherwise, this just comes with the territory.

As far as your financing options, you can do anything you want. Keep in mind that the builder may tie certain incentives into using their lender, so make sure you are aware of the requirements. Even still, you can buy the home with any mortgage from any company. If the builder offers the best deal after considering their interest rate, fees and incentives, then go for it. If not, who you choose is your prerogative.

Your realtor can help you sort through all of the information, good luck!

You can pick whomever you want for a lender. However, some builders illegally tie incentives to the use of their very own mortgage company.
Your realtor may be able to look into local bond money programs for down payment assistance. These will have income limitations as well as geographic locations.
Good Luck!!