What website/application would you recommend for spaced repetition of vocabulary?
I've found the changing Windows logon screens quite nice, since every other day or so there's a new beautiful picture along with a few bubbles of text in German, enabling me to learn a few new words (though I'll probably forget most of them).
You don't want ready-made decks except at the very beginning. Once you get past words like "mom" that have very obvious usage, these decks aren't great because they lack examples and structure.
Instead, one should use Anki to make their own decks with words that they find whilst learning the language.
You can, and I have, make your own Memrise courses as well. I'm better at remembering to visit a website than I am at remembering to open a program. It's a silly difference, but I almost always have a browser open and every new tab I open serves as a reminder. I always fail to remember to open/use software. The times I've tried converting to Anki rather than relying that Memrise will continue to be available, my study time per week dropped by about 95%~.
You actually can use anki online, it's ankiweb.net. You can't modify decks on the website but it works for studying daily cards. Otherwise I use the mac osx or ios apps.
If you want a Spaced Repetition vocabulary quizzing for German, you might try: https://eardoor.com I created it just for listening practice and spaced repetition vocabulary practice: 1 hr/ 1 day/ 1 week. No sign in/sign up required.
Anki. See my other comments in this thread, but I can vouch for it after using it for almost 2 years for Korean and now Japanese kanji.
The manual documents it well, and I recommend you only use a ready-made deck for about 3 months at the most. After that you should be making your own word decks.
I like readlang a lot. They have a very nice browser integration allowing you to read text and get dictionary lookups in-line. It does cost $5/month but it's very well made.
I've found the changing Windows logon screens quite nice, since every other day or so there's a new beautiful picture along with a few bubbles of text in German, enabling me to learn a few new words (though I'll probably forget most of them).