Really comes down to personal preference as far as a Head Unit goes. Any good reputable brand is a good choice, Sony, Pioneer, Alpine, etc. Sony makes some really decent head units in the $100 price range. I would suggest trying to find the dash kit that has you clearance the cassette hole and install the adapter piece to retain use of the original bezel. The aftermarket ones tend to have problems with vents and fitment in general.
As for speakers, we would really need to know how much you want to spend. There are several great options out there for speakers, it just comes down to how much your willing to pay and how you would like your system to perform. Keep in mind that any 4X6 speaker isn't going to be GREAT by nature of the design, but 4X6's that perform pretty damn good are out there!