One of the most common designs starts with laying out a grid of dots. These can be in a square grid or in a triangular grid. The artist then draws lines of chalk snaking around the dots. The lines can be continuous or have breaks (implying depth—that sometimes the line goes over or under another line).
Here is another, but with the initial dots laid out in a hexagon. If you trace the white lines you'll find that they correspond to the faces of an icosahedron. For this one I decided to make the lines continuous.
After doing a few abstract designs I decided to see how far I could take the concept. So I made a crocodile. Or, as I like to call it, a Crookodile.
And here is a Rango-lily (i.e. rangoli + lily).
Lastly, I took a cue from this website and tried making the Salt Lake temple. In my imagination it was a lot more spectacular that it actually turned out to be. In reality a kolam this big just looks like a cross-stitch pattern. Oh, well.
 See http://en.wikipedia.org/wiki/Kolam and http://en.wikipedia.org/wiki/Rangoli (both of these seem to be largely translations of the equivalent pages on the Hindu Wikipedia; neither is very readable).
 See http://en.wikipedia.org/wiki/Kolam#Patterns.