The Ring's corruption forms

[Legate of Amon Lanc]

Maybe I could add something more. Concerning just the "result" of corruption, Gollum (or Bilbo, or Frodo) would ultimately become something similar to the Nazgul (only weak and somewhat - just shadows, not any "great pale kings of horror"). The thing is, that they - probably from a large part due to their halfling nature - never reached the state of ultimate consumption by the Ring. As we know, Gollum even almost repented. Gandalf says:

Originally Posted by FotR, Chapter 2: Shadows of the Past

Even Gollum was not wholly ruined. He had proved tougher than even one of the Wise would have guessed -as a hobbit might. There was a little corner of his mind that was still his own, and light came through it, as through a chink in the dark: light out of the past. (...) Alas! there is little hope of that for him. Yet not no hope. No, not though he possessed the Ring so long, almost as far back as he can remember. For it was long since he had worn it much: in the black darkness it was seldom needed. Certainly he had never "faded". He is thin and tough still. But the thing was eating up his mind, of course, and the torment had become almost unbearable.

So, Gollum is not fully "consumed" by the Ring (as we are told plainly in the movies); he is crippled, but "not wholly ruined". He did not wear the Ring as often later - only kept it close to him, and the Ring could not tempt him, because Gollum had no more ambitions at that time than not to be seen. And in the black darkness of the underground tunnels, the invisibility was not needed. If he did wear the Ring all the time, I'm convinced that he would become a shadow and once Sauron would have called for him. But he did not, nor Bilbo did, and so they eluded the "transformation", to use that word.

It is also important in some aspects that the "fading" the One Ring causes is somewhat different in nature from the "fading" caused by the Nine Rings (or the Seven, for that matter - btw, we know the Dwarven bearers also never "faded" due to their toughness). The Nine are meant to enslave the bearer, being "channels" to Sauron's will, but the One is that will that enslaves others. This is a slight difference and maybe some won't agree with me, but I believe it plays its part as well. What I want to say is, somewhat roughly speaking, that the Nine or Seven have the intention (now that the One was forged) to make you a Nazgul, while the One makes you fade just as a "side effect".