I am completely in favour of legalising assisted suicide, I think it's one of the most fundamental human rights to be able to decide when and how your own life should end.
The issue of financial skulduggery is easily circumvented - for those people who elect for assisted suicide, then simply slap 100% death duties on their estate. If you're not mentally capable of making appropriate arrangements before your suicide, then you're not capable of making a rational decision about ending your life.