The first Bilbo shown here is from the production design of the Rankin/Bass animated show of the 1970's. Although this design was softened and changed for the actual show, it survives in posters and artwork used to illustrate the tie-in print of the book.
The second Bilbo is how the hobbit actually appeared in the cartoon. He was voiced by Orson Bean, who did a fine job interpreting Bilbo's naivete, innocence, and a sort of English delicacy that borders on fussiness, without making him sound immature or childish.
The third Bilbo is from Ralph Bakshi's The Lord of the Rings. I read somewhere recently that his design was based on (if not actually modelled by) Billy Barty, and seeing his stubby fingers and squinchy eyes one can notice the resemblance. The film suffered from severe plot and time compression, and coupled with the unsubtle nature of animation, Bilbo was reduced to a cameo comic turn.
The fourth Bilbo is of course the great Sir Ian Holm in Peter Jackson's The Lord of the Rings. Sir Ian was already an old hand in the legendarium as he had played Frodo in the BBC radio production. His interpretation of Bilbo in all phases throughout the films is simply beyond compare.
The fifth Bilbo is from the Sierra Entertainment video game adaptation of The Hobbit. I think the design, while distinctly individual (especially the hair style!) hearkens back to the Rankin Bass conception. I enjoyed this game; even its story embellishments were not too far-out, and the writing shows a competent familiarity with Tolkien's work.