Well as you know Rob I like the medevil style, so I would opt for a john Smith's style texture pack myself. The things I like about it are the different textured wood types, the relitive similarity (but still different) looks of the stone, cobble and bricks.
I like this pack since there are many different looking blocks but they all follow a similar theme...even mossy blocks tend to blend well with other stone blocks, making randomisation and material variety easy to do.
The only warning i would give is to watch out for the wool...some texture packs offer cool looking blocks in place of useless wool colours like pink for example. However a pink wool block used as thatch on a roof looks wack to other players who don't have the same pack lol....
I like the idea man, keep it up and I look forward to seeing what you come up with. Unfortunately I have no experience in creating textures so i will be of little use to you in that capacity...
Edit: Oh and a 64/64 res would be nice
Nonny