Introduction
May 9th 2013 - Today we have released the Visual Micro plugin for Visual Studio and for Atmel Studio 6.1
See our beta downloads list and forum for beta versions and more information.
Atmel Studio is based on Visual Studio 2010 and is entirely FREE :)

Visual Studio Pro and Ultimate Alternatives
In March, Microsoft ended the free program that provided Visual Studio Professional Free for 3 years for Arduino programming. Now (beta) we can use the Atmel Studio 6.1 (may 2013 version) of Visual Studio for free.
This page previously described Visual Studio free offers, now this list is restricted and not so useful. However, here is a summary of what I know to be still available...
Bizspark - Free VS Ultimate for companies younger than 5 years and less than $1m profit p.a.
Dreamspark - Free VS Pro for Students
At the time of writing it appears that these Microsoft schemes offer others benefits to the free VS pro and are for a limited time. However it looks like you get to keep the software after the schemes end