Is there a way to provide customer feedback on Android products?

I was wondering if there was a way to let Google and its partners know what I like and do not like about their products. I think providing constructive criticism will only help Android become better in the future. I can certainly rate and review Android apps on the Google Play Store, but those only apply to specific apps. There does not seem to be a way to comment on Jelly Bean itself or the Nexus devices, for example. Is there a way to send feedback via email? If email is not appropriate, I would be open to other methods. Thanks!