The Elemental: Fallen Enchantress beta has been available in early form for some time now through Stardock.com accounts, but if you plan on owning the game through Steam eventually anyway, now's your chance to have it on there and play the beta through it too.
As of last evening, the beta went live on Valve's service; unfortunately you can't transfer beta access from your Stardock account (should you have one) to it, and getting said access requires the $40 pre-purchase. Remember Fallen Enchantress is free to anyone who bought Elemental: War of Magic early enough, so this applies to a select crowd.
Fallen Enchantress, if you're just catching up now, is a sequel of sorts to 2010's RPG-strategy game Elemental: War of Magic, and is said to be a marked improvement over that title in just about every way. It releases this autumn.