As I watched the text appearing all over the page it struck me how fit for purpose it is for brainstorming (or whatever it's called nowadays), whether you're in the same room or not. It's fun and it generates a bit of healthy competition; you feel compelled to get your ideas down before someone else has the same idea.
Etherpad was bought out by Google a while ago but alternatives, using the same technical system, spring up all the time. Until recently I used http://typewith.me but I'v just checked and this has been superseded by Primary Pad.
You'll need a way of sharing the web address for your pad with students. I'd say either stick it in a Moodle page or put it up on the SMART board. If it's a really long address, you can make it shorter (and so easier for others to type in) by pasting it into the box at tinyurl.com.
If you've got students using SMART phones in class you could always put a large QR code on the board for them to scan instead of typing in the address (create a qr code in 2 clicks here).