I'm a confessed Gingeraleaholic, and I like it in cans (more pop & fizz) and heavily iced.  I also like it in a medium-sized glass; too big and it melts too quickly and dilutes; too small and it has to be refilled too often.

I also tend to live in warm climes, so condensation is an ever-present problem, and that's doubly-true here in Florida.  And, to be honest, dripping ice-cold water droplets on my bare chest isn't one of my favorite things to do in life.

So, years ago, I decided to get serious about the whole coaster problem and went around buying up different types of cork from supply houses and cork coasters from import shops — and it was all a bust.  The cork just couldn't absorb the heavy amounts of condensation that was being dripped on it.

The alternative was gluing a kitchen sponge to the bottom of the glass.

Then I thought of giving a couple squares of paper towel a try, but this time with a twist.  I'd obviously tried it before, but it's too light and lifts up with the glass.

This time I slipped a CD disc in between the folds — and it worked!

It has enough weight to keep the square down, and its flat surface doesn't interfere with the drink's stability.  You put it about 2/3rds down, leaving plenty of paper towel above to sop up the mess.  I use two 'full-size' squares of paper towel, folded down to about 5" square, just perfect for the disc.  The first few times you use it, purposefully place the glass on the corners to flatten them down.
      

You also need the right glass.  It has to have a relatively flat bottom so the paper towel can do its job.  If it's too concave, you'll get the dreaded drippies.

As far as glass versus plastic, I'd say glass definitely has more condensation, so I've almost always used plastic.

When mine eventually cracks (and they always seem to), I start haunting the grocery stores, Wal-Mart and K-Mart to find a replacement.  It's usually not an easy task because most glasses have fairly concave bottoms.
 

And yes, a coaster made of paper towels is pretty ugly — at least compared to a dark circle of cork embedded in a smooth walnut-grained encasement with Waldorf Astoria printed in gold leaf.

On the other hand, it actually works.