You don't need these unless you are going to take the Software Defined Radio (SDR) option but they do come in handy for just about everything you'll ever want to do. The main thing to remember is that whatever hardware platform you choose, if you are going to do digital signal processing (DSP) you're going to want a fast processor because lots of DSP is quite heavy going for the computer.
Software is available from many sources and you may even have to buy some, god forbid.
Most DSP software contains a fast fourier transform (FFT) spectrum analyser, waterfall display spectrograph (frequency & amplitude/time) and audio record/playback function from your radio via the soundcard or from files on your selected storage disk. The more exotic packages offer additional capabilities such as auto correlation and other advanced noise reduction techniques.
If you are planning to take the SDR option you'll probably get a DSP package with the receiver, then again, maybe not. The USRP is made to work with the GNU Radio suite on a Debian Linux operating system (OS). WinRadio G3xx receivers are primarily made for the various Micro$oft Windows OS and come with standard or optional DSP packages, with limited resources and support for operation under Linux. For other SDR models, check the manufacturers sales information regarding hardware/OS/software requirements.
Some links you might find helpful are:
Spectran - FFT and spectrograph
Winrad - FFT and spectrograph with (limited) SDR control
Audacity – Audio recorder and editor with FFT
SetiFox – FFT and spectrograph
Spectrum Lab – FFT and spectrograph