It would be great to have single relay modules, both the high powered and solid state relays.
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The problem is that that would be a really big waste of even an X socket… 
The problem with the 4-relay is that if you only need one it is a waste of some money and it’s a lot larger component you have to manage.
So, I’m working on my own module that will hopefully combine each of the things I need into one module.
@ Pintsize.me - your getting the idea! When somebody comes up with a need for a module that does not exists - make it the DIY way! There are lots of requests in this forum for modules that don’t yet exist. Often, the requestor does not take into account the feasibility of producing any given idea on a production scale, so many requests will simply not ever be done by GHI or other manufacturers, even though they are great ideas. That’s where we come in to fill the gap. Hopefully you’ll consider open sourcing anything you do come up with.
Of course if the e-blocks were still available that would be great with the e-block module or the pins on the CerbuinoBee, then the stuff that would be a waste could still be done as e-blocks which would speed things along. Another option would be to offer the e-block devices headerless so that we could connect them to breakout modules.
Then I could take a piezo, relay, LED, and button eblocks and connect them all into one module.
Now that I see the $20 quad relay has been discontinued and replaced by the $60 16x relay module. I think the ~$10 single suddenly makes sense.
it isn’t a waste of a socket if your project only needs one relay.
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Agreed
How about a daisy chain version of a single relay module? No more socket utilization issue.
That wouldn’t work if you want to keep isolation, which I love personally.
Why would one relay be isolated but not when daisy chaining?
I’ve seen a practice of adding a down stream socket, that is almost straight through, but shifted one pin on. This means that the relay will connect to pin 3 of the main board socket. But the pass though socket on the relay module will shift the pins on one, so, although the next relay will also connect to pin 3 of the pass through socket, the first relay module will present pin 4 from the main board as pin 3 of the pass through socket, and pin 5 from the main board on pin 4 of the pass through socket.
This will mean that you can connect up to 4 relays on a X socket and up to 7 relays on a Y socket, all transparently via a daisy chain…
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@ GMod(Errol) - Interesting technique!
I meant the DaisyLink protocol. 
I can’t take credit for the idea. I saw it being used in a snowfall led tube circuit, combined with charlieplexing, so you can connect up to eight strips, each containing seven leds.
See here: FAST Finally Affordable Snowfall Tube - doityourselfchristmas.com
That would also work. My way would just be easier and cheaper…
I think $10 is the sweet spot for a 10A A/C relay. Adding the cortexM0 and parts for daisylink would increase cost - and keep in mind if you really want multiple relays you can always go up to the 16 relay module.
… That said I can see to make it daisylink would be for high power, triac switching like scenarios. Ie, power a 240V heater element at 50% duty cycle by passing simple values through the driver. There is a chap on here making a brewing computer, that kind of thing warrants the added complexity. And while you’re at it you may as well make them chainable. But that is another beast entirely.
A possibility would be a DS2413 1-Wire Dual Channel Addressable Switch in connection with a relay and a led…
That would also be a nice solution, but it would still add at least $2 to the cost of the module.