filtering giveaways

Well, you can search for a game using the mini search box on the left on the giveaways page.
You can also use this in the url to set the giveaways to level 5+
http://www.steamgifts.com/giveaways/search?level_min=5

You can find more search parameters here and here

There is also this extension which I believe makes these search parameters easier to use but I'm not sure.