I tried out a few (Smart Draw, ChiefArchitect, Google SketchUp) and ended up liking SmartDraw the best. It ran $197, and it has paid for itself over & over again--best money I've spent for my own use in the home design process. But it really comes down to user preferences. Smart Draw allowed me to design floorplan layouts and elevations interior & exterior. I was also able to import the plans my designer would send over in PDF format and manipulate them. I could export my designs as well to PDF or JPEG formats (which helped with posting on sites like GW for advice).

Some programs you buy & download over the internet allow either a free trial period (SmartDraw offers 7 days free) or a money back guarantee if you don't like it (Chief Architect does this).

Feel free to do a search by my user name and you can see some of the designs I did with SmartDraw for myself and others. I've got some in the 'Building A Home' forum as well as in the 'Kitchen' forum. Here's a few that may not be posted (click on the image to see it larger):

Here is a link that might be useful: SmartDraw Website

It seems everyone has a different goal when using CAD software so it is impossible to recommend one that would make every homeowner happy. But for quick visualization of small projects, especially exteriors and complex roofs, nothing can match SketchUp. It is a favorite in grade school and in architectural firms.

SketchUp sections

SketchUp importing plan

SketchUp walls

while sketchup is a great FREE 3d program that is pretty user friendly, I wouldnt say it is good at drafting plans. However it would probably be fine for getting things laid out so you can take to your architect/drafter. Pitched roofs and some other complex modeling seen on many houses posted on here would also not be the easiest thing to accomplish for a newcomer to the software. However I would recommend it for a 3d modeling side of things, and one of the other listed programs for the drafting.
There are people in my firm that will use sketchup a lot for mass modeling (and unfortunately, final renderings...looks very cartoonish in my opinion), but that is because they are not good at our real program that I use everyday, Revit Architecture 2011-2012. This, however, is not a DIY program.

The key issue is whether you are trying to design the house or create construction documents - two very different goals.

Many homeowners tend to think of the "design" of a house as a "plan" when, in reality, it is just one of many ways to help someone to visualize the actual design and it is not always a very good one for complex designs. Plans, elevations, details and schedules work well for builders because they aren't trying to evaluate the overall design, only build the house one piece at a time.

IMHO nothing compares to SketchUp for preliminary design at any price (SketchUp basic is free, SketchUp Pro is $495, the Student version of Pro is $49/year and a trial version of Pro is free.) Since it is unlikely a homeowner will have the knowledge to draw a set of construction documents I would suggest sticking to preliminary design and hiring someone with the proper experience to do the rest.

A SketchUp model can be easily looked at in plan view especially with the Section Tool shown in the link below. It doesn't take a skilled drafter much time to enter the information from a SketchUp model into a 2D CAD file because the drafter can use the tape measure tool to find all of the dimensions (if they are not already labeled in the model) and it is possible to import a 2D version into almost any CAD program (Pro has DXF export and the free version will need a plugin script that is available free online.)

SketchUp may seem intuitive and for a grade school student it is but for a house designer it has so many valuable features that it requires taking a course at a school or online to be used effectively. You should study and experiment for a month before starting to design your house. There are books available at Amazon and online courses from SketchUp and from SketchUp for Dummies/aidanchopra.com. When I open a SketchUp model from 10 years ago I am surprised at how few of the features I was able to use. There is never an end to learning with any CAD program. Each new version of the software adds incredible features.

SketchUp view inside model

Sketchup is a great tool, particularly if you have have a CAD background. However, it isn't a dedicated house planner and I'd say @Renovator8's about right in estimating a month's learning curve for using it as a home design package.

Just starting out, I'd encourage you to look at the Home Designer line of software, particularly the Because it's dedicated solely to house design, it's a lot friendlier (IMHO) for people just staring out and you can create a house with wizards in a few minutes, then refine with pre-built design elements. The 3D visualization is pretty good, too.

So instead of spending a month mastering a generic tool like Sketchup, you can spend that time playing with your new virtual home. And if you get serious, you can upgrade through the more sophisticated versions all the way to Chief Architect.

Here is a link that might be useful: Home Designer Software

I fully understand the advantage of designing a house by sizing and assembling pre-built elements using a CAD program dedicated to that approach.

But I think these programs greatly limit the final design even in the hands of an experienced designer. I believe the design of a house should be focused on spaces and how they relate to one another and to the outdoors. And I find that SketchUp allows me to start with spaces and add elements making them more realistic as I proceed. I confess it can be a chore to add all of the realistic elements needed to sell the design to a client but I couldn't arrive at as good a design without SketchUp.

Tonight I plan to draw an existing house and add a new screened porch. Hey, times are tough. The roof intersections will be very difficult to design well because the new roof touches a gambrel, the side of a lower sloped gable and a second floor porch. I know of no other CAD program that would allow me to quickly test roof options until I found the best one. I may print some views of the model for the builder and be done with it.

Good luck with whatever you choose to use.