Here's the problem: It's not make and model that matters. If you are programming newer radios like the Professional Series or Commercial series, most any laptop or desktop will do. The latest versions of these software packages run fine under Win 7, and there are reliable USB cables available.
If you need to program older radios like the M1225, that software is a bit finicky. I found it won't install on my Win 7 laptop, but works really well on my older desktop which is a Win 98 machine. It also has a real serial port which makes finding and using cables for older radios much easier.
Now, if you need to run something even older like the GM300 software, I found that it runs fine in a DOS window on my XP desktop.
But older stuff like the early Radius software wants to run on DOS only. I haven't personally tried it on my XP computer, but I know it will boot to DOS so it should work. Just in case, I have an even older Win 98 desktop sitting in the closet that will run pure DOS just fine.
So, in summary, make and model is mostly irrelevant. What you need is most likely going to be a Win98 computer with at least one real serial port. What I would do for that is to find a local computer shop that repairs and sells older PC's. If you only need a desktop, there are a lot of them out there in good shape for cheap. Laptops are becoming more and more scarce because things like keyboards, hard drives, and displays tend to break under portable use. Batteries wear out. People won't put any money into fixing older laptops so they get junked.
I get spoiled with the Pro and Comm series radios because I can take the laptop anywhere and just climb in the cab of the truck or car to reprogram. I only have three or four M1225's to care for so I don't mind pulling them to program on the bench. Everybody's situation is a bit different so you have to consider which radios you're doing, how many of them, and where they are located.