Mars gets all attention, but Venus is actually more hospitable in the clouds.
http://en.wikipedia.org/wiki/Atmosphere_of_Venus "Despite the harsh conditions on the surface, the atmospheric pressure and temperature at about 50 km to 65 km above the surface of the planet is nearly the same as that of the Earth, making its upper atmosphere the most Earth-like area in the Solar System, even more so than the surface of Mars. Due to the similarity in pressure and temperature and the fact that breathable air (21% oxygen, 78% nitrogen) is a lifting gas on Venus in the same way that helium is a lifting gas on Earth, the upper atmosphere has been proposed as a location for both exploration and colonization." A manned flyby mission to venus was planned in the 1970s http://en.wikipedia.org/wiki/Manned_Venus_Flyby Harry
