i suggest magic fishing, you can only cash in your earning once a day but it will add up. i strongly suggest magic fishing over anything from golden tokens.
after that gem hunting at linden labs is good, as is earn2life, and dragons and princess all can get you lin you will have to work a bit at it.. but it can work.
i should point out i have yet to get earnings from earn2life so i can not vouch for them..i have from all the others.