Phras.In

This is an interesting little site for learners particularly at higher levels, who are interested in collocations, etc.  It's very simple.  You need to have two possibilities of words/ collocations/ sentences that you want to test, you type them in and the site will tell you how many hits there are for each (ie which one is in more common useage) and also show you the contexts that they appear in. 
Here's an example I tried with the rather loaded word 'spinster' vs 'single woman'

You can see which is more common!

This can also be used to good effect for comparative grammar.  I put in 'I went to China' and 'I have been to China' and it was interesting to see that the simple past is 4 times more common than the present perfect, but also to have lots of authentic examples of the (problematic) latter tense.  It's concordance for the common man!

I think that this will appeal to a certain type of learner, who is very interested in the language itself, but you could give them pairs of possibles to try out for a homework task.  It's also nice to ask them to put in phrases you have taught to give them a wider context for using that language. 

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Tut Pup Spelling Site

This is a brilliant site for young learners who want to practice English spelling.  Basically, it's a fairly bog-standard spelling bee type programme.  You hear a word (at a level that you chooose, ranging from 'Easy Peasy' to 'Uh Oh') and you spell it. 

What makes it oh-so-much-more engaging is that you are in competition with a real person in real time somewhere across the globe.  You get to see their 'codename' eg Red Turtle 567 and where they are from (shown by a flag) and you have a limited time to spell the words that are said.  This is my game with Pink Cow from Belgium!

If you register, the site will record your victories and you can win 'medals' for various combinations of wins.  Clearly it's aimed at younger children and adults will probably feel patronised by it, but there is something incredibly motivating about knowing that you are competing against another real person somewhere out there.  My kids really love it!  You can practice maths on it, too.

Learning Chocolate.

Great name for a site - not so sure that I love it as much as the other kind...
This site opens with the introduction:

Welcome to Learning Chocolate! This web site aims to help students to memorize vocabulary in an easy and efficient way, by using pictures, sounds and games. Try our games and enjoy learning, like eating chocolate.

.. and that's what it does - it's essentially a picture dictionary -

The great thing about this site is the range of activities that you can do with each picture – it gives you the pronunciation, the spelling and the meaning, and you can do different games to help you to remember.  These include listening to the words and matching them to the picture, a dictation exercise, and other matching exercises.  Here's a sample page:

This site will probably appeal to younger learners at lower levels, but here’s the rub – a lot of the vocabulary is REALLY obscure – I didn’t know a lot of the ‘cuts of meat’ words, and I’m an adult, educated native speaker of English!  The options don’t seem to have much focus – so we have (at one end of the spectrum) feelings – sad, surprised, happy – elementary level words –and then, at the other end, we’ve got the life cycle of an insect with words like ‘pupate, emerge and cocoon.’  There’s no indication of the frequency or usefulness of these words, (although I guess that some common sense in translation would tell most people that cuts of meat aren’t common conversation starters unless you’re a butcher!)  The other problem is that the vocabulary is obviously decontextualised, although, as a lot of it is concrete nouns or action verbs, perhaps this isn't so important.  It might be a nice site for younger learners to do  -maybe learn one selected section as a homework task. It could be useful for spelling.  Try it out.