Hulk - the Rampaging Hulk from Toybiz Incredible Hulk series 1, it's under-articulated as well as a bit pinheaded but I use this as my primary Hulk due to its height and wide build
Grey Hulk - from the Hasbro Hulk video game series, this is a great representation of this incarnation of the Hulk. It's too bad the Green Hulk from that same series was so short (shorter than this figure in fact) or else I would have included him in the collection.
Smart Hulk (aka The Professor) - from the Toybiz Incredible Hulk Transformations series. A really nice sculpt and paintjob.