I would also recommend HP, I have mine for 19 years now (HP-11c), and dropped it seveal times, nothing happens! Only changed batteries three times! The LCD starts to deteroriate not at one corner, but is still usable...........
It works differently though than normal calculators, so it needs some to get used to. There is a financial version: HP-12c I think, but there are others. Check eBay, or ask Mr Wong at Fotografix, secondfloor of Chinatown Center (or something like that), the shopping center in Chinatown, just next to that chinese style bridge (it also has a McDonald on the groundfloor)........he collects these HP's, good luck!
HS