I agree with what Disasterpeace just said about getting in as many nooks and crannies as possible. For my recent release, first thing I did was create physical copies (I used a service I'm sure some of you know of called Discmakers), mostly because people were actually asking if I had any merch at shows and I was sick of saying no. Not just to make some extra cash but also because it's important to make a lasting impression, and sending a CD home with an audience member is a great thing to do. Yes, this was a little pricey, but I actually should have it paid off soon, and I didn't have to charge too much to do it (At $5 a disc, I had to sell about half of them to get back what I paid. And that's $5 for 6 songs, about 33 minutes of music plus art, etc... seems like a decent deal to me.)
Next thing I did was use CD Baby for digital distribution. For about $30, and a small percentage of each download, they distribute your music everywhere. And I freaking mean everywhere -- iTunes, Amazon, last.fm, etc etc etc -- except somewhere like bandcamp. This was solely for exposure. I think it's important, as others have said, to consider that there might be people out there who do not think much deeper than, "Let's see if this is on iTunes. Oh, it's not? I guess I'll never find it." Obviously enough, you can also sell physical CDs through CD Baby if you want, but I chose not to because they take a cut that was not worth it to me. I'm still selling the discs on my site, and that seems good enough to me for now.
Finally, I distributed the album (albeit a special edition with Cheese N Beer) through bandcamp as well with a "Pay What You Want" price. Once again, this is mostly for exposure and to give people as many options as they want. The PWYW is nice for anyone who has already bought the CD or generally expects their music (not just chip) to be free/cheap. Bandcamp makes a big deal about how they are not exclusive with rights so you can continue to sell through iTunes, etc....
So honestly, why not do any of these things? I realize that some are more expensive than others upfront, and that's a good enough reason not to. But if you can afford all of them and care about exposure, I think figuring out a way to make as many outlets as possible work together can only help you.
first one I've missed in forever!