If you are desperate about getting rid of them, you can send them to a bot such as "Dota 2 Dispenser" (http://steamcommunity.com/id/dota2bot?l=english) who will take them and send them to people that request a copy. I have used the one mentioned above and it was quick and easy, and they are no longer filling my entire inventory! 
Do this. You'll help a hundred newbies get started with playing Dota 2.
Alternatively, you can list the Dota 2 gifts on the Steam market http://steamcommunity.com/market and sell them for $0.01 each. You'll quickly be able to earn $1 that you can spend on whatever you like. Valve only allows 200 sales per year iirc, so don't do this unless you don't have anything to sell on the market regularly.