I have the Travel Trac RealAxiom. It is controlled by the computer to provide realistic resistance compared to the grade of the course. It takes into consideration a weight factor (I have it set at 30 pounds abocve my body weight to account for bike and gear) and tells you your speed, watts, HR if you get a wireless strap, cadence, etc. Keeps track of your virtual miles and climbing etc and lays it out for you for performance comparison. It's like a Computrainer, but not quite as advanced. I find it is overall pretty realistic on the "flats" and that the "climbs might be a tad easier but the "descents" are harder. It seems the way I have it set up sort of averages out. Of course, wind resistance isn't factored in either other than increasing the weight above your body weight.
It has video courses that you can buy and ride (2 come with the machine when you buy it). Or you can ride preprogrammed non-video courses or upload/enter your own course data to make a virtual (non-video) course.
I really like mine and love to be able to target my training to specific areas and watch the improvement over time. I can tell my power, cadence & HR has improved since I started using it.
Here is what it is http://www.performancebike.com/shop/...slisearch=true
I'd still rather ride outside though. I got an Edge 305 for Christmas, so I'll be able to still keep a lot of my stats going, but I'll lose the power angle come spring. Although I'm using SportTracks and it "calculates" the power output based on weather conditions and aerodynamic profile (kind of). It's not really that accurate, but it should be a reasonable comparison over similar courses to watch the trends.