There is a site for this (I think its something like bitcoin.cc.cz or bitcoin.cz.cc) but the problem is how to deal with people who don't pay. Do you take the money before hand, how do you decide if there are ambiguous terms of payment, etc, etc.
I think we should collect the money before hand... Put your money where your mouth is so to speak.
I suggest we also have a board of competent coders decide what bug fix is worth what - and perhaps an accountant type to look after the overall value of the fund - similar to how a condominium board takes care of itself.
If you own a lot of bitcoins, it is in your best interest to give back to the community and improve the client - I don't think we'd be pulling any teeth here.
Perhaps one of the competing bitcoin mining pools might want to "donate" 1% of it's collected fee towards this charitable cause, and might attract more miners because of it.
Or perhaps the newly minted bitcoin millionaire (mentioned in another thread) might want to donate 1,000 or so to get things started!? (If he does, his new nickname is "Bitcoin Bill"

)
$3k USD can go a long way in the world of outsourced programming.