For starters: the Kryptos Helper page. This page displays the text of all four panels, lets you highlight certain letters (e.g. all C's and Q's, or the letters in BERLIN), switch from encoded to decoded text, and highlight K4.
This site is in its infancy, so do not expect much yet!
o The Kryptos Helper page.
o A page with most of the known hints and clues (and a timeline)
o The decoded Kryptos text.
o The Vigenere tableau used by Kryptos.
o The original Kryptos sheets/charts used by Jim Sanborn
o A positioning helper tool
o The Kplus25 Helper page.