My $.02:
Wile I definitely concur that the stock speakers are terrible, the real issue with our trucks is that they're too darn loud. Nature of the beast, really, especially with the diesel. So, the easy way is to get some decent speakers and crank it up, and maybe a stronger head unit and/or an amp. But that's solving a noise problem with, well, more noise. The real solution is to yank the carpet and throw in some sound deadening material. There are tons of products out there that basically do the same thing, so take your pick. That being said, I have owned 3 bricknose trucks and have always taken the lazy way myself, lol. But I have a buddy who used to have a 89 std cab, and he put DynaMat everywhere underneath the carpet. I tell ya, it makes the difference in a big way.
You've definitely received good advice on the speakers. Screw brand names and all the hype; go with what YOUR ear likes. I'm a big Sony speaker fan for this reason. Hardcore car audio guys generally thumb their nose at Sony stuff, but screw 'em. I know what my ear likes to hear.
As for head units, the first thing is to determine what features you do and don't want. Personally, I'd skip Bluetooth in our trucks. Again, they're just too noisy, so using it for cellular phones probably won't have the desired effect. And as for using Bluetooth to listen to music, you can but the audio quality is never as good as a physical connection and it drains the battery on whatever is playing the music like mad. Sure, you can plug that device in to charge, but why not save the hassle and just plug it in to the head unit directly? For that reason, I recommend a head unit that has either a 3.5mm (aka headphone) jack in the front, or a USB port, or both. This will allow you to plug in any kind of music player (smartphone, ipod, mp3 player, etc) you want. Even cheaper is to buy a small thumb drive, load it with all your music, plug it into the stereo, and leave it. It used to be head units with all these features were pricey, but now even the cheapest WalMart units offer them.
Oh, and Pandora is an online music app that let's you listen to music for free. You sign up, tell it what kind of music you like, and it makes a 'channel' just for you that you can then tailor by letting it know if you like or dislike the song being played. Pretty cool. I use it at work all day. I also have the app on my phone, so in the truck I just hook up my phone to the stereo (using a headphone-to-headphone cable), start the app, and head on down the road. It's nicer than using an iPod because it plays both stuff it knows I like and stuff I may like based on what I told it, that way I find new music to check out as well.
Mike