What to do with Desura keys?

Public spreadsheet?
It's the best way to attract greedy people, someone could just export them for their personal use and empty the spreadsheet.
Make giveaways for the games you're allowed to give here (if any), and dump the rest somewhere, preferably not all together.

offer them in your giveaways, group/whitelist?

if you offer them in public most people will grab them just because they are free.

I'm in the same boat. I need to clean up my groupees wall, like 200 to 300 desura keys in it.
Maybe try gog.com forums, as many people there are drm-free and would rather not use steam, so win/win maybe?

Don't trust users to do the proper cleaning /respectful taking; you should know what they would do, given no control or supervision.
Sadly, most (but thankfuly not all) humans will take advantage of all and anything that can be exploited. This is why we can (often) have nice things.

It'd be hypocrit of me to offer to participate; I do have a Desura account, and I've enjoyed collecting and playing some of those.
I'm not sure how to help you, but it's probably a good idea to encrypt, censor, cover or hide the keys IF you're willing to part ways with it.
Since you can't do giveaways, you could create some and hid them inside, OR hide them in other gibs you want, OR just select people you like what they said/done and just casually gift something to those you enjoy as a token of apreciation.

If it's just too much work, it's sign you're getting beaten by lazyness! fightback with all your might! don't let yourself taken and crushed, as lazyness takes the best of us, and lays waste and chaos afterwards, also favors the ninjas and bots, while damages the good folks that actually aren't cheaing, don't have speed internet or are just otherwise engaged, like Sheldon used to say :P

sorry for typos, lazyness like I said, it's 1am and I'm supossed to go to bed.. or it could be on purspose and I've hidden something.. mhwahahahaaa!

cry. It's what I do
I forgot my password years ago and the company went under, so support doesn't respond

I have 1100 games on desura, downloaded them all, with screenshots and everything. :x
http://www.desura.com/members/lugum/games

I be willing to trade you cards for the ones i don't have and can check ones that aren't used.
I can't remember if it would say key unused or just already owned.

You can post a list and add people who want a game then give them the key.
Or randomly put some in your giveaways.
If you put them in SGT giveaways, people would need to have an SG account to get them.