awesome question. but i can't choose just one. so here they are

from hitchiker's guide ect (the books, the old tv serials and radio programme): marvin the paranoid android

and from doctor who i like k-9.  i also enjoy cybermen and daleks because they are pretty awesome, especially in the older episodes....when the cybermen looked as if (or probably were) made out of carboard boxes and vacuum cleaner tubes.

i also enjoy C3PO and R2D2.  and dot from spaceballs is always a kick. :)

oh and of course wall-e. he was so darned cute.