A few more options, on the positive side:
- c'est (bien) possible — (quite) possibly
- c'est pas impossible — there's a chance / you certainly have a point
- certainement — sure, I'd believe/allow it
- a priori — seems so, currently
neutral:
- en quelque sorte — sort of
- plus ou moins — more or less
- oui et non — yes and no
- oui mais. (and you are supposed to explain what the condition is at some point)
on the negative side:
- si on peut dire — somewhat, but we can't really say so
- mouais — mhmm + a very small ouais
- bof — maybe kind of, but still