My Pioneer is the CD-SR77. A decent drawing of the remote can be found here and you can buy one from many online resellers.

It's an infra-red remote so it has the problems of other IR remotes in that if you've got bright light shining directly on the remote sensor, forget about it. Ambient/reflected light hasn't caused me problems, but when direct sunlight hits it, it's useless. It's a small annoyance and certainly a wired remote would be nice, but the only wired one that works out-of-the-box are the Sony's, and they're not "steering wheel remotes" they're "steering column remotes." So I chose location/ergonomics over 100% reliability (mine works about 98% of the time, it's not all that sunny here.)

As for functions... Well with Frank's IR trans kernel, whatever you'd like it to control. And I actually hacked up the IR trans to allow for double the number of functions (minus one) by choosing one of the buttons to be a "toggle button" which toggles what each button sends. So there are 11 buttons, and normally 10 of them control things like next/prev track, volume, menus, source (tuner/player), info mode, etc. Then I hit the toggle button and the buttons all become the numbers 0 through 9. This lets me do searches from the steering wheel remote (a little clunky to remember which button means which number, but it works for me.) So the number of remote BUTTONS is 11, but the number of functions can be more if you don't mind hacking a little.

Really it's a matter of personal choice. My Pioneer works good for me and some others, but some people like the convenience of the wired Sony stalk remote. I just think I'd have to mount it in an odd location on my car.