The links above provide all the info you need, but I'll give a relatively uninformed nod to VectorWorks. We've been using it for 2D and rudamentary 3D CAD work at my lab for almost a decade now (since way back when it was called MiniCad in version 4 or 5; it's at 11.5 now), and although it's not a perfect piece of software and it's not as powerful as something like SolidWorks, it's a decent package and easy enough to use.
Versions 8 and 9 were, in my experience, a little shaky and seemed to have an undue number of bugs as a result of the move to OSX, but version 11.5 so far has performed pretty well on both our 10.3 and Win 2K/XP machines, and I'm willing to recommend it.
Depending on what your situation is, it's worth noting that educational licenses for v11 require a stupid USB dongle that, while not hideous, is something I really frown on. The full pro license apparently doesn't need the dongle, or so I've heard, but this is still a big step back from previous versions, which haven't used a dongle since at least v6, maybe earlier.