Spotted this outside my window today. Looks like an orb-weaver, but I can't tell whether it's a regular garden spider or not. What species could this be?
This picture was taken in Bangalore, Karnataka, India.
Looks like an orb-weaver ..
I agree! This spider definitely belongs to the genus Argiope, though, due to the angle of your provided image, it's difficult to be more specific than that (if I had to guess, A. anasuja).
The confidence in my genus suggestion comes from the stance the spider is displaying. Spiders within the Argiope genus carry a common nickname of "signature spiders", due to the fact that they'll intertwine additional webbing within their web, called stabilimentum, that, given the design of the support webbing and the spider's stance, will allow for the spider to appear much larger than it really is.
If you can provide an image that reveals the top of the abdomen, a more confident species suggestion may be possible.
Is this a common garden spider?
From the looks of it so far -- yes, this is a common garden spider.