The poster above speaks a lot of sense- if you are only planning on using them for mixing at home, with friends, and for recording mixes etc I would definately research all the options before spending a ton of money on Pioneer CDJs just because they are Pioneer.
They do make great CDJs no question, but so do other companies. For what it’s worth I sold my Pio CDJ900s (in my username pic) to swap to the Denon SC2900s when they came out because they are in my opinion a better unit in every way except for not having HID for software control (their midi control with Traktor is however excellent).
It will largely depend on your budget but in my opinion if you want USB capable players I would consider the following:
Lower Budget: Pioneer CDJ400s, Reloop RMP3alphas - none of these have waveforms at this level, but to be honest if you are used to Traktor then only the waveforms on the 3 players in the last catagory are going to cut it.
Medium Budget: Denon Sc2900 / Sc3900 - IMO these are better (features AND build quality) than the CDJ900 and miles ahead of the CDJ850, and cheaper than either.
Money no object: Pioneer CDJ900nexus, CDJ2000, CDJ2000nexus - the 3 Pio players with the full LED screen, definately the ultimate solution to go truly laptop-less with software-style browsing/visuals.
If you are happy to burn & use CDs then I would probably disregard all of the above and pick up a pair of CDJ1000mk3s (no usb port) as I still hold that these are the best built DJ cd players made, and the only Pio players that came close to justifying their price.
Using a laptop-less setup is a lot of fun, there are far fewer visual cues available to you so you do feel somewhat more involved.
I would just keep in mind that you are going to have to keep your music well organised. In this regard I would definately consider one of the players that has the ‘network link’ feature (CDJ900 & above/sc2900/sc3900) as this will at least give you the option of connecting a network cable to your laptop and use it as a music database/browsing screen (running either Pio’s Rekordbox or Denon’s Engine software) should you wish.
This is different to using traditional DJ software as the hardware (the CD players) are actually playing the music still (not the computer), the computer is simply acting as a storage & browsing facility- this means you can use pretty much anything for this as system specs are not much of an issue (I often use a crappy 11" netbook for this) and certainly in the Denon’s case you can use an Ipad instead if you prefer.
For me the bottom line is that if you make the switch to CD/media players and mixer you’ll be set for the future, then if you decide to incorporate software again further down the line it is easier (and cheaper) to do so whilst still maintaining the option of stand-alone functionality. It is a big investment but I simply couldn’t go without the sheer versatility of CD/usb decks now.
Just do plenty of research (read reviews, watch videos, basically google the hell out of every option out there!) before pulling the trigger, I can’t stress this enough. This way you get the equipment that is right for you- at the end of the day if you put a great mix together nobody listening to it is going to care what make of equipment you recorded it on (in my experience only other DJs and equipment manufacturers care what you are using, and they are but a tiny percentage of the people listening to your music).
I’ve owned or used a fair chunk of the above players so I’d happily give you some more detailed thoughts on them where I can 