Mitt Romney has been taking a lot of criticism, from fellow Republicans as well as Democrats, for refusing to make public his tax returns before 2010. As he's correctly pointed out, there's no legal requirement for him to do so. But almost all recent presidential candidates have released more returns, including his father George when he ran for president in 1968. The only other recent candidate to provide just two returns, Senator John McCain, has filed less detailed financial disclosure forms for the many years of his service in Congress. Even nominees for cabinet posts much provide three years of tax returns to the Senate as part of the confirmation process.
As McClatchy newspapers have pointed out, most members of Congress who have called for Romney to release his returns -- including House Minority Leader Nancy Pelosi of California and Senate Majority Leader Harry Reid of Nevada, both Democrats -- don't make it a practice to release returns themselves.
Some prominent legislators who do routinely release their returns include Senators John Kerry and Barney Frank of Massachusetts and Senator Claire McCaskill of Missouri. For a list of those who responded to to McClatchy's request for information on their returns (either directly or through other news media), see this other article. Thirteen Democrats and four Republicans were willing to reveal at least one tax return.
It should again be noted that members of the House and Senate do file financial disclosure forms that provide some information, though not as detailed as that included in tax returns.
I agree with Public Citizen and others who say there should be more disclosure from politicians across the board.