Looking at us being at the end, my 3 most likely to die characters are:
I have a different reasoning on each one... I'll probably be wrong because other than Herschel I haven't guessed much right.
I'll give you Bob (he seems pretty expendable), and maybe even Beth (although I think she's probably safe), but you really think they'd kill off Carol in the finale? After that last episode she was in, and with whatever issues between her and Rick, and her and Daryl? She's become a fairly-interesting character, and I think they have more stuff for her to do in the future.