Vocabee - free vocabulary learning tool

Vocabee is a learning tool built on the Leitner system, the method of repeating new imput in 5 cycles at increasing intervals. Designed for learners of any subject and language, it lets you repeat the content you enter in one of two modes:

Using the "gezielt lernen" mode, study a selected unit to prepare for an exam, storing the content in your short-term memory.

Choose "langfristig lernen" to study using the 5 cycle method, to store the content in your long-term memory.

This tool, launched in January 2011 and currently in beta, was developed by SeitWerk. The makers promise that vocabee will remain free, and they guarantee that what you store there will still be available in 10 or more years. They also promise that they have a lot of ideas up their sleeves to improve on the app.

There is currently a lot of nice free content already available for English and Business English. It was collected by an advanced learner of English (whom I know), who got most of his input from studying at Language World in Starnberg.

Applications for spaced repetition flashcards

There seem to be (at least) three major good online flashcard providers on the market for EFL. They all work using the system of building your memory by review based on spaced repetition.

Phase 6: http://www.phase6.co.za/opencms/Homepage
This service has been around since 2002, and it's probably the most professional. It is basically an empty tool that lets you create your own content. Available for Mac OSX and Windows, but the Mac version is in Beta. The blurb says content includes English for ESL, Spanish, other languages and academic vocabulary and terminology (science, law, medicine, economics)

Their blog says that they have introduced "The “i-tunes of education” concept:

"As of June 2009, we’ve got the following (publishers) on board: Diesterweg Verlag, Klett Verlag, Cornelsen Verlag, Langenscheid Verlag, Springer Verlag, C.C.Buchner Verlag, Mentor Verlag, and Martin’s Little Helper."

Anki: http://ichi2.net/anki
This service is free and Open Source. Very friendly video introduction. Available for Windows and Mac OSX, for jailbroken iPhones and the iPod Touch. This is primarily for writing up your own vocab, but it seems to be geared to content sharing communities, so for example teachers can push contents to students.
I've seen this recommended on Das Englisch Forum.

AZ6-1: http://www.az6-1.de
This service was developed by a father-daughter team, and it now seems to be used with PONS content. Besides serving Mac, Windows and Linus, it has a mobile app, but only for phones running Java MIDP 2.0. The focus seems to be on ready content that you can buy in small topical modules, geared to content at German schools. You can add your own content, as with the others, too. A USP seems to be the colorful skins you can put on your learning environment, which appeals to the kids.

Do any of you have experience using any of these, or other similar flashcard applications? Thanks for sharing tips!