Ralph Nader has entered the presidential race, though his effect this time will be trivial as Nader last much of his support during the 2000 Presidential campaign when many feel his 5% of the popular vote effectively threw the race to George Bush in his win over Al Gore. Gore won the popular vote handily but Florida's razor-thin vote margin eventually was decided in Bush's favor, giving him the electoral votes and win.
Personally, I've lost most of the respect I had for Nader feeling that his economic philosophy is more anti-corporate than it is pro-people. Corporate abuses - even in the past when they were arguably more flagrant - pale in comparison to the disadvantages people face if they cannot participate in the big corporate economy that drives our world. Roadblocks of the type Nader favors that put legislation and regulation in the way of corporate progress hurt the poor, because they raise prices on products and make it much harder for companies to deliver goods and services effectively. There is a minor safety advantage but it's trumped in most cases by the cost disadvantages.
I'm sure there are exceptions to this - where safety is worth the cost to the corporation - but I don't think Nader advocates for intelligent ROI analysis. Rather, like many people who are mathematically challenged, he simply won't address the huge costs to society of regulatory structures that inhibit innovation and profit.