On stock/inventory homes, it depends on the stage of the development. Often the last homes in the subdivision are the inventory homes and the builders sometimes discount them heavily in order to get them sold so they can get out of the development. HOWEVER, those homes typically have more amenities built into them (the builder adds all the bells and whistles when he builds them so he can show potential buyers what is available), so their starting price is higher. That can end up meaning that you get a discount over the as built price, but it's still higher than the base price in some cases.
We have had several builders go out of business over the past few years. As a result, we can sometimes find partially finished homes and homes in developments where only a few homes are finished and the rest of the development is questionable as to when it will be finished (so you may be living in a construction zone for awhile or you may have a second builder who comes in and builds a different style of home or a much cheaper home) may on the surface seem like great deals, but if in a few years you want to sell and you are competing with a builder who is still building or someone who sold later homes at a much lower price point, you may have an issue.
One thing that the builders and developers do not negotiate on is discounting the price if you don't use a Realtor, since the commissions are built into the marketing budget, not the sales price. When you buy directly from the builder/developer, their salesperson is working for the developer and protecting his interests, not yours. The Realtor is there to protect your interests and to help negotiate any decreases in price or perhaps the addition of amenities. The rule though is that you have to identify the realtor when you first sign into the development, otherwise the developer will not let a realtor help you later.