Bloodrage amplies all three main sources of damage (magic/pure/physical) done by the target that is bloodraged
There are very few exceptions to this: Blademail return damage, Nyx's Carapace, Techies Suicide, Viper's Corrosive Skin and Warlock's Fatal Bonds are not amplied as outgoing damage. So if you Bloodrage a Techies and he uses Suicide, it will not do more damage; however, you can still Bloodrage the person Techies is targeting Suicide with, and that target will then take more damage.
A target that is Bloodraged and has Blademail turned on, will not reflect more damage BUT if you cast Bloodrage on the hero that is targeting the Blademailed hero they will take more damage. So if Spectre has Blademail activated, and you Bloodrage Spec, she will not reflect more damage. If you Bloodrage Tinker and he lasers Spec with Blademail on, Tinker will take more damage.
Apart from the few aforementioned spells, and a few HP removal based spells, Bloodrage amplifies nearly everything.
Also, in the future use the Dota 2 wiki, it is arguably the best wiki for any game I have ever seen. It should have nearly all the answers you are looking for.