While I highly recommend trying to solve the Archer Easter Egg yourself, Reddit has done a good job of summarizing it and providing hints and ultimately the solution. And even though a number of the clues are hidden in plain sight during the show, they still utilize many interesting ciphers and codes to make the hunt challenging.
Perhaps my favorite cipher in the hunt was the embedding of text in an audio channel. Contestants were directed to a youtube video from previous clues. From there the audio is extracted and stored locally and then loaded into Sonic Visualizer. To view the embedded text, select the Layer Menu and then choose “Add Spectrogram”. For this example, the text “RPH8GBIMBU1WF0RVHXIUDWYQHIDR” was embedded in the audio. This text was then used as a passphrase for a Vigenére Cipher.
The Vigenére Cipher was just one of many ciphers used such as ROT13, Base64, and hex encoded ASCII. A great website for web-based cipher tools is rumkin.com.
All in all, the Archer Super Easter Egg Hunt is educational as well as fun. Oh, and the show is pretty good too.