Hire an actual, licensed (both state and patent bar) attorney. They may charge you a bit more than these invention sites, but they will actually help you protect your intellectual property.
These other services usually can get you a provisional patent, but unless this is done exactly right it is not going to provide you with any protection, and it is not really what you need to take your invention from the concept stage to production (where you actually plan to make money off of the idea).
The NOLO press offers a good book about how to patent ideas ("Patent it Yourself"), and this can help you be a more informed consumer when working with your IP attorney, but if you really want to protect your design, you need to hire a lawyer.
(I know that customers don't come here to be told "go hire a lawyer" but I would hate to see you throw away $5k on a service that isn't going to give you what you really need).
Again, you want a lawyer that is not only licensed for the state, but also with the Patent Bar (USPTO).
You can find local attorneys using the State and local Bar Association directories, or private directories such as www.AVVO.com; www.FindLaw.com; or www.Martindale.com (I personally find www.AVVO.com to be the most user friendly).