There's also always the old school of thought that considers the humanoid form the most practical one for sapient speices. If that assumption holds true, then whenever there was an evolutionary pressure towards sapience, there would also be a simultaneous evolution towards the humanoid form. At least the very basics would be there: vertical orientation, with a set of manipulators held up high, free for using tools, and a set of limbs for movement down below, plus a sensor cluster on top of everything. And if the starting point for that is a creature that lacks manipulators and has to develop them from locomotion-type forelimbs (and not, say, from jaws or tongue or somesuch), then a bipedal humanoid-type structure would be a very natural result. Certainly all the nonsapient "template" forms available down here on Earth would have been conductive to the evolution of just such a sapient form.
But that's a very old school of thought that doesn't have much evidence on its side. All the evidence comes from a single planet, after all... Sure, it can say it's making a logical argument, but again, that's by the logic of a single sapient species! Other species might have different kinds of logic, to which we are inherently blind.
Me, I like to think that in the Trek universe, the "The Chase" aliens indeed are responsible. At least for the prevalence of DNA-based life, and probably also for the prevalence of humanoids like themselves.
Timo Saloniemi