Portraits of the Presidents from the National Portrait Gallery
Smithsonian created this website as a way to collect all of the portraits from past and present presidents, as well as a little information about each one. Click through the names on the left to get to that president's page. Some of the portraits also have an enlarged version, so you can take a closer look.
Wikipedia List of US Presidents
This is another great place to go for a quick of US presidents. All of the presidents listed on this Wikipedia page are color coded based on party affiliation and have a portrait thumbnail. From this page, you can also find out length of time in office, the vice president during his term and what his previous government office was.
The Official White House Website and Mobile App
Keep up with the current administration on WhiteHouse.gov, also available in a mobile app. From here, you can learn about all of the current issues our president is tackling as well as various ways to engage with the administration on Facebook.