Are there any Greek islands close to Ios worth seeing?
 

Where else can I go close to Ios if I only have a couple of days? Is Santorini too far?

In your other post you wrote that you arrive in Greece on the afternoon of Jul 7th, and depart on the morning of Jul 11th. You will need to be back in Athens on the 10th to make your flight home. That means you will have only two days for Ios and will spend much of the rest of your time in Greece travelling on ferries and transiting to/from ports.

If you want to add even more time on ferries, there are ones leaving Ios for Santorini in the morning and others returning to Ios in the evening. Check in the travel agents when you get to Ios to see what is available.

You could go to Paros and Antiparos....In Paros you could visit the villages of Lefkes and Nousa absolutely charming places. I stayed in Paros for 2 days and I wish I had had more!
And at Antiparos you could do the caves - stalagtites and stalagmites.

Depends how long you have ......quite enjoyed Siros and Mykanos......you would need at least 2 days in each island to get a feel of the place.....

NZwanderer, the OP has a total of four days in Greece, and wants to spend two of them on Ios. He is now asking about a day trip from Ios to another island. No point in giving advice (re Paros) that would be impossible to follow. ;-)