To achieve what you want you will need a Macbook. You are not allowed under the Mac OS X EULA to run their software on a machine that is not made by Apple.
... you are granted a limited, non-transferable, non-exclusive license:
(iii) to install, use and run up to two (2) additional copies or
instances of the Apple Software within virtual operating system
environments on each Mac Computer you own or control that is already
running the Apple Software, for purposes of: (a) software development;
(b) testing during software development; (c) using OS X Server; or (d)
personal, non-commercial use.
In regards to virtualisation software you have three options, Virtual Box, Parallels and VMWare Fusion. Each of them will do the job I personally use Parallels, and haven't used VMWare Fusion.
If you are running virtual Machines, you will need as much RAM and disk as the machine can take. You also have the option of running iOS simulators as well if required, but you will need the Retina Macbook pro to test them at anything close to native resolution.
Personally I now use a fully pimped out 13" Macbook air, and it ticks all these boxes for a very reasonable price.