As for now (June 2011), the latest version is VB10.
All stars that are in hydrostatic equilibrium are on the main sequence, where outward thermal pressure from the hot core is balanced by the inward gravitational pressure from the overlying layers.See related questions
The most massive star (The star with the most mass) is a star in a super star cluster called R136 or RMC 136 in the Large Magellanic Cloud (LMC). [See related link for more information] The star, for all its fame has a rather unremarkable name of R136a1. It has the mass of about 265 -> 300 solar masses (256 x the mass of the Sun - See related question). See related link [BBC] for a pictorial size comparison. It is a blue supergiant with a spectral type of O3. Because of its mass and intense luminosity (10 million times that of our own Sun) it, astronomically, will have a very short lifetime in the millions of years rather than billions. At the end of its life, R136a1 will explode as a supernova and because of its relatively close distance to Earth (165,000 light years/ALU [See related question] it might be visible during the day. This question is about the most massive star (mass), not the largest (Radius) [See related question]