I think people blame God for things they don't understand out of fear of the unknown. God created us to worship and love him, but He didn't want an army of "yes-men", incapable of thought. He created us to have imaginations and creativity, which is where many of us get carried away. Imaginations opens the door to evil thoughts, and creating on our own gives us a false sense of independence. It is when we become so full of our own accomplishments that we fail to acknowledge God.
I don't think of temptations as others. We have choices to make and, due to our inflated egos and false independence, we make the wrong choice, on our own. True, there is evil offering bad ideas, but we make the decision. The same as the two year old who wants to touch a pretty, porcelain doll. Mom says no and slaps the hand. The child will repeatedly try to touch the doll, getting hand slapped. After MANY bad decisions, the child learns NOT to touch the doll. We need to learn to seek God in all decisions, before they are made, and listen for His guidance, AND seek God immediately for wisdom of how to correct our bad choices.
I don't think we need the devil to sin. In this day, we can get up and make bad TV, radio, internet, chat, etc... decisions on our own, while the devil takes a long break... to prepare for when he will send an attack on each of us.
I also think evil is allowed to exist to truly show us the beauty of God's love and peace. We probably would not appreciate His goodness as much, without seeing the bad.