There are not all that many around, in "original artist" form.
The only individual tracks I can think of from Rock bands are "Wring That Neck" & "Contact Lost" by Deep Purple & "Laguna Sunrise" by Black Sabbath.
There are artists / bands that mainly do instrumental work, such as Jean Michel Jarre - Oxygene & Equinoxe etc.
For instrumental versions of songs originally released with vocals, you may be looking at orchestral covers of the tracks or stuff like Two Cellos, who again cover well known pieces.
Two of the ones mentioned above:
https://www.youtube.com/watch?v=7kHFj8eWF4E
https://www.youtube.com/watch?v=8IZ92b5Na6U
Edit; a bit of lateral thinking... If you just want instrumental "background music", have a browse through the guitar tabs on Songsterr. Many can be played as audio - and quite a few have all instruments plus something to fill in for the missing vocals.
(Ther vary through extremely good to naff to absolutely abysmal, but there is decent stuff on there).
Some examples - you may have to copy & paste the links.
Hit the Play button near the top of the screen once a track has loaded up.
http://www.songsterr.com/a/wsa/green-day-boulevard-of-broken-dreams-tab-s92866t3
http://www.songsterr.com/a/wsa/guns-n-roses-sweet-child-o-mine-tab-s23t2
http://www.songsterr.com/a/wsa/eric-clapton-bad-love-tab-s5010t3
http://www.songsterr.com/a/wsa/zz-top-sharp-dressed-man-tab-s2433t0
http://www.songsterr.com/a/wsa/beatles-day-tripper-tab-s354t0
http://www.songsterr.com/a/wsa/limp-bizkit-take-a-look-around-tab-s11443t1
http://www.songsterr.com/a/wsa/pearl-jam-jeremy-tab-s15691t1