Are you looking to keep the CD/tape deck or are you okay with just a CD player? How much do you want to spend? Do you want to play MP's? How about a remote control? (don't laugh remotes are just as useful in a car as they are for your TV)
I think Pioneer CD players are about the best on the market at this time, they look nice and are very easy to operate. I even put one in my moms car and she can hardly turn on the computer. You can find much better deals on decks online than at best buy/circuit city/ect... However you will have to put it in yourself and you will probably only have the Mfg. warranty if something breaks.
Just upgrading the deck will make your stock speakers sound much better so I would wait to upgrade the speakers until after you install the new deck. You probably will be fine with the stock speakers, not to mention they are the hardest and most expensive part of upgrading a sound system.