If I have a length of stocking stitch, and want to break it up with raised ridge every few inches, what would be the best way to do that? A couple rows of just knit or just purl? Or something else? :??
A few rows of just knit (garter stitch) or just purl would work well for a ridge.
Either way works. They have a different look so you might want to swatch it to see what looks best for you. 
A welt would give you a larger ridge, but you can decide how large or small to make them. I’ve just recently heard of the technique myself.
Here’s a how to article with pics:
http://www.community.knitpicks.com/xn/detail/1984936:Note:41552
Hope that helps.
Thanks! It’s coming along wonderfully 
That welt is neat (though not the look I was going for this time)… I wonder what sort of pattern would call for a welt?
I realize you’ve probably committed to a certain method already, but another thing you could probably do is a few rows of reverse stockinette (After doing knit-purl-knit-purl, stick in a purl-knit-purl-knit).
If you really want it to pop, the pattern I’m about to start does the above, but then goes a step further by knitting the top and bottom of the reverse section together, making it more of a horizontal tube going across the work.
I actually saw someone making a HUGE bag (think beach baggish) with welts (the welts were also a different color) And it was beautiful. I didn’t know what they were called at the time, but then I saw this article and knew that’s what she had done.
If you read the article it says that welts can also be used for a drawstring if you do a YO to created a hole, I think that’s so clever!
Along the same lines… if I’m knitting st st in the round, will doing a round of purl sts give me the same result of a raised ridge on the right side of my work?
Yes.
You’ll probably notice that the row you purled, doesn’t perfectly line up at the end of the “row”, because knitting in the round, is actually worked as a spiral. This is called a “jog” It happens when you add new colors to make strips. I know there are several methods for making “jogless stripes”, I woud assume the same principles could be applied to making stripes when changing your stitch pattern.
Maybe someone else here knows for sure?