What kind of router work do you foresee yourself getting into? 2D, 3D?
There are many good cadcam packages out there.
You will undoubtedly get MANY opinions on what software to buy, so I might as well be the first.
I suggest you check out www.onecnc.com This comapny sells several cadcam packages. Like many companies, they have demos available from their site. They also have one of the most informative User forums I have ever experienced. In addition, the makers of the software are extremely responsive to customer input and are very helpful in regards to learning and understanding the software.
Even CNCZone has a section for OneCNC. Check it out. You will find tons of info there.
Buy once, you will probably be set for years.
Hope this helps