I've been wondering about certain positions that arise often. To help me understand them, I would like to study the joseki moves. Since printed joseki dictionaries are out-dated very fast, I'd prefer an electronic database if possible.
This is a kind of wiki for joseki. This system has the big advantage of offering explanations, deviations from joseki and refutations,... But I don't know how complete or accurate it is.
Kogo's Joseki Dictionary
Kogo's Joseki Dictionary is certainly the best known resource in the west. It's an SGF file that contains a huge list of common and uncommon joseki moves including some comments, some even with the game where they occurred.
It is reliable in general, even though there are some mistakes (that are probably difficult to spot unless you're dan or even high dan level).
KJD is included in Eidogo online, so you don't need to download the SGF anymore.
This joseki database is condensed from a database of pro-games. One problem with this approach is that it doesn't contain any explanations or refutations.
It also offers some joseki memorization system, but I never tried it myself.
Brugo is probably the only dictionary maintained by pros. It includes a few variations not seen anywhere else and tends to be very reliable (as far as I can confirm this).
There are a few tools (like a joseki quiz) rarely found anywhere else.
I use this one:
This one is the best in the sense that you immediately see how the board will look like afterwards, so you can choose proper Joseki according to your current context. But some Josekis (like 5-3) are unfortunatelly missing there.