Some common leaks are a bad o ring or a hole in the evaporator next to the radiator. The best way to find the leak is with a leak detector like this one:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=170007139973
I would replace the accumulator because it absorbs moisture from the A/C system. Also vacuum the A/C system before recharging it to remove air and moisture. You can leave the A/C system under vacuum overnight or a few hours to see if it will hold a vacuum. If the A/C system won't hold vacuum then you know the A/C system has a leak. If the A/C system has quick connect fittings, there might be oil around the fitting where the o ring is leaking.