Sachys: Well, in terms of what I said about a "utensil", an example might be the hammer of thor (though not a perfect one - my brain will not let me access gubbins as it should tonight and hence this bit of research has been most unfruitfull!
If you can't find anything, but CAN find a parrallel deity from another culture that fits the same bill as Ian... then that would be a good alternative,
Sorry to jump in here, but I believe one of the symbols associated with Janus is a key.
As for beginnings and endings, only the Indian deity Kali pops into my head at the moment, but it's late, so sorry if I've missed the entire gist of this discussion.