I know an 'other' option has been discussed and I think something like that would be good. What I tink might be better though is to have an optional Comment Box, so you could add something like 'I picked this one because...' or 'I like this one but...' or 'I kinda liked this other one too...'.
I thinks comments like this would really be helpful in Fellowships where the Big Boss wants to know whether or not s/he should create something for the fellowship, say, what type of pond to make. These comments would probably only be visible to the creator of the poll and not for everyone to see.