Short of God coming down herself to say "Howdy y'all!" what would it take to make you a believer in God?
Not necessarily the God of the Bible or any religion in particular, just a Supreme Deity of some sort, call it Ra, Thor or Chaos.
What kind of proof do you need?
First you need to define what a God is.
What kind of proof do you need to believe in life after death?
If there were no connection to the life after, there couldn't be any proof that I can think of. If though, life after death included 'spirit' people communicating back with people alive here, then you could set up some kind of experiment. It's up to the claimant to explain what they can do and to think up a satisfactory protocol.
What kind of proof do you need to believe in mental telepathy?
One hundred simple words written on individual cards. Cards are placed in a box. Person A in room A, person B in room B. At 10 minute intervals (e.g. 10:00, 10:10, 10:20 etc) experimenter selects a card from the box, hands it to person B. Person B then attempts to 'transmit' this information to Person A in the other room. There is no communication between the rooms. At each 10 minute interval person A writes down what they think the word is. A hit is the exact word (which is why we keep them simple, to remove potential for spelling errors, assuming the words are 'transmitted' as sounds rather than the actual letters). Person A must guess more words correctly than we would expect by chance. If this succeeds the experiment is then repeated, but with a stricter protocol, to ensure there was no room for cheating and no mistakes in the first experiment.
let's limit it to those few things.
What would be proof enough?
To get a good feel for how these kind of experiments are constructed, and the thinking that must go into them, take a look at the log of challenge applications for the million dollar challenge, here:
http://forums.randi.org/forumdisplay.php?f=43&sort=lastpost&order=desc
It makes very interesting reading.