I know this works in CS3, but I'm not sure about CS. If I were you, I would try creating a calligraphic brush. Under the brushes palette (window>brushes), click the icon to create a new brush. Select Calligraphic brush. You can then edit the shape and angle of the brush by turning the circle/changing up the width. If you want it to be square, rather than round, drag the Roundness slider to 0.
You could also play around with making an art brush. Create a shape, drag it into the brushes palette, and go from there.
Again, this works in CS3, but I'm not sure about CS, so I hope this helps!

Thanks Alissa -- but I'm not sure how this would keep the lines parallel and make them look like they recede and come forward again. Would I warp the line once I make it?

I've found two ways to create ribbons but neither is quite right:

1) Use the blend tool to create parallel lines within a ribbon. With this approach, however, all the lines are a uniform thickness and I need to have them varying thickness. Can I alter this somehow? Perhaps I can select an individual line and make it thicker? I'm going to give that a try next.

2) Wrap stripes of varying widths around a 3D object. I'm not sure if this will work, though, as I need a shape that has mulitple bends. Perhaps I could create a customized 3D shape to use? I'm just trying to get my head around how to do that as the lines should kind of look like they are meandering across a landscape.

Thanks for your suggestions!

I think...

I found this tutorial that looks like it'll work:
http://www.blog.spoongraphics.co.uk/tutorials/illustrator-tutorial-create-a-colourful-abstract-wavy-ribbon

I love that blog.

If anyone has other suggestions, however, I'd love to hear them!

Veerle's Tutorials are a winner.

http://veerle.duoh.com/blog/comments/creating_a_ribbon_in_adobe_illustrator/

Yes, I like Veerle's as well.

So now I have a new problem. I created parallel rectangles for the stripes, selected all and then used OBJECT > ENVELOPE DISTORT > MAKE WITH MESH to shape it.

The problem is that once I alter the shape of the envelope I can't ungroup the envelope and return the individual rectangle objects (i.e. the stripes). I need to be able to change the colours of these individual rectangles that made up the envelope after I've altered the shape as the colours will not be finalized until much later.

Any ideas of how to select each individual rectangle that was grouped together in the envelope? I've googled this one a lot and can't find anything.

Thanks again.