MeldaProduction MRhythmizer does stop/start too but I would still try the free options first, aside from tapestop, and the original glitch, TAPEBRAKE is a newer freebie http://www.kvraudio.com/product/tapebrake-by-wok/details Never tried it myself because Tapestop works fine for me.

Anderton
You don't need Sound Forge or Reaper. Like true analog  tape variable speed, speeding up shortens duration and raises pitch, while slowing down lengthens duration and lowers pitch and Sonar can do this. The most common variable speed tape effect I did by far was speeding up the final mix by 1 or 2%, which of course also raised pitch by 1 or 2%. This technique easily accomplishes this function, as well as the "Chipmunk effect" and a bunch of other cool stuff.

The speed change can be up to four times faster or slower, and you will not hear digital artifacts. In other words, it’s just like using tape except that with this technique, the speed change is not continuously variable. The thread referenced by scook has that and other "varispeed" techniques.

1. Open the clip in the Loop Construction window.
2. From the Clip drop-down menu, enable Stretch On/Off.
3. Move the Threshold slider all the way to the left (0%) so all the markers disappear. This is very important.
4. The two right-most fields adjust semitones and cents respectively. Do not enable the Pitch button! That will just confuse things. Cents will adjust +/-49 cents which should be enough. If not, for example if you need to make the pitch 70 cents sharp, set semitones to 1 and cents to -30. (For Chipmunk effects, set semitones to +12 .)
5. Render the clip, and it will reflect the pitch/speed changes you made.

Cool. I haven't played with the loop construction thingie yet but I'll check it out. Honestly I was starting to get the impression that it was an outdated way of doing things from the way people talk abotu it but this is a good excuse to see for myself. I also just remembered why this is on my mind. there is a weird breakdown in my current project that I'd like to try some time/pitch warping at.
 
Any chance that tempo changes done in the LC can be made to alter the tempo map of the project? I'm guessing there is because from what I know of the LC it's suited for beat matching and what not.
 
Either way... thanks. And thanks to everyone. A plethora of ideas leads to a plethora of options. Cheers.

I would say the main downside of this approach is not being able to incorporate actual speed increases or decreases, or really any kind of variable effect at all, unless I'm misunderstanding.

Sanderxpander
I would say the main downside of this approach is not being able to incorporate actual speed increases or decreases, or really any kind of variable effect at all, unless I'm misunderstanding.

You understand correctly, it's not possible with the loop construction window approach (at least that I've found). If I need continuous pitch shifting for something like sound design, I'll load a sound or track into Dimension Pro and vary the pitch bend. That technique is also covered in the thread referenced by scook.

Ah fair point. Why would you choose this approach over simple ctrl+slip edit then? I thought it did the same thing?
EDIT: oh dumb, of course that affects only tempo, not pitch. Isn't there an algorithm in there that allows you to do it without actual time stretching?

Sanderxpander
I would say the main downside of this approach is not being able to incorporate actual speed increases or decreases, or really any kind of variable effect at all, unless I'm misunderstanding.

I think I've seen gradually speed changes done with it in some of the vids (perhaps in one of Craig's). I really do have to take a closer look at the LC sooner than later. My current project is supposed to be all about explore the more advanced topics and odder tools in Sonar (as well as test out various configs of my external equipment for the optimum input and... well to fully learn how some of that crap works too) so I think I'd better find a good spot to get the LC in there somewhere.
 
So far I've really nailed down the basic principles (and honed me playing of) my padKontroller, learned how to use AD2, got better at working in the PRV, hooked up my Line6, tweaked it out for bass and learned how to reliably save presets on it, got a handle on the new comping mode, messed around with some of the newer effects, worked out some better methods for writing/tracking/archiving, got better at handling system resources and just general got to know my way around all the menus and shorcuts better.
 
What I need to do now is hook up my mixer, see if I can get my darned DX-7 working as a controller, test all my mics for different applications to see what will work best, test about a hundred input variations for my guitar tracks, learn the Matrix View, learn more about all the various synths, learn how to sample properly, learn how to use automation lanes effectively, set up FX chain modules and track templates, figure out a good way to capture sound from other sources like the net or off old tapes and stuff, etc, etc... and I guess now try out the Loop Constructor.
 
Then take another crack at mixing. So I've got a lot on my mind. lol

The Waves Sound Design Suite is now on sale for 400 bucks. It includes the Soundshifter, among a whole load of other useful stuff (like L1/L2/L3, MondoMod, SuperTap).