If I was nerdy enough to have a "favorite engine," it would probably be the Unreal Engine—not necessarily for its technical achievements (though you can't say it hasn't been an essential tool for developers in the past decade), but for its accessibility. The easy-breezy development kit has been especially kind to indies, and because of that, some brilliantly creative games have been built on the engine. Now Steam's flogging an Unreal Indie Bundle, and for $20, it's actually got a pretty admirable selection of games.
In the seven-game lineup, the stand-outs for me are the hypercute Dungeon Defenders and slick-looking Sanctum - these are two tower defense games I've dragged numerous pals into playing the past couple of years, and I'd feel pretty pleased with myself if I could drag the readers of PC Gamer into playing it too. Meanwhile, I'm also looking forward to giving Primal Carnage a whirl. While our preview in October last year thought it decent despite not seeming quite fleshed out, it's half a year onward, and I'm dying to see if those promisingly savage dinosaurs have cut their teeth on the beta stage and become truly, frighteningly awesome.
The other games included in the package are Q.U.B.E., The Ball, Unmechanical, and Waves. All up, the games are worth about $80, but in the Steam bundle? You can get 'em for twenty. Though there isn't a specified end date for the promotion, it's warning that it'll be around "for a limited time only."