Ribbon

I use ribbon a fair amount.  If using it on a fondant cake, it's really easy to just dunk the ribbon in water, wring out the excess water then stick it on.  No pins, royal icing, etc necessary.

I also like to use ribbon because it is beautiful and can also cover up any issues that occurred at the bottom of your fondant if that happens.

I have found that how you attach it to the cake depends on the material it is. I haven't tried dunking it in water and attaching it. I'll have to try that next time. That sounds like a great idea.

Mpaulson, does that work for many different materials?

I have used icing before and long pins for more delicate materials that are kind of slick/smooth (I'm not sure you would want to use water on these but I haven't tried). I actually like the long pins and they can look cute too and add to the character of the cake.

When it's time to cut the cake, you simply take the ribbon off the cake. It's very common, especially at weddings.
 

I love the ribbons on around the borders of the wedding cakes. They look very pretty!!!
 

If the ribbon can get wet enough, it should work but there are some materials that may not work (i.e., sheer ribbons, etc).  Also, you don't have to worry about the ribbon falling off once it dries; the fondant becomes sticky enough when wet that it'll stay attached.

I just stretch the ribbon around the bottom of the cake and then attach it with some royal icing.  I will then put a pin in to hold it until it dries.  After I pull the pin out I will generally stick a bow on, with royal icing again, to cover the join.  It will then remove very easily when it is time to cut the cake.