I do most of my conditioning these days with kettlebells, either doing complexes or just timed sets of swings. Currently, I'm mostly doing: 15 seconds swings / 15 seconds rest Work up to 10 minutes of that, then start mixing in a heavier bell one set at a time until the heavier bell replaces the lighter one for all sets. Then repeat.
Barbell/kettlebell complexes can be endlessly varied: http://70sbig.com/blog/2014/11/chalk-talk-11-barbell-complex/
Or, just burpees. You can do descending sets: 10, 9, 8, 7 ... 1, with a fixed 30-60 second rest in between. If you want to really hate life, superset the burpees with dumbell/kettlebell swings or snatches.
Dan John's "The Eagle": from http://danjohn.net/2011/06/the-four-steps/
Ross Enamait's "Magic 50": http://www.rosstraining.com/articles/themagic50.html His books "Never Gymless" and "Infinite Intensity" are heavily conditioning focused, and have enough ideas to keep you busy for a lifetime: http://www.rosstraining.com/products.html Warning: these are harder than anything else on this list.
Stupid title and overpriced, but great short+hard conditioning workouts: http://www.amazon.com/100-Conditioning-Workouts-Modern-Viking-ebook/dp/B008XO4XVW/
Even more ideas in this reddit thread: http://www.reddit.com/r/weightroom/comments/tcv9m/training_tuesdays/