Paul Carter just posted an interesting article on conditioning on his website.
Although the strength numbers he lists are quite high for non-powerlifters, the conditioning program looks good for anyone. I don't know about you, but I'm not in the 400 bench, 550 squat, 600 deadlift range. I'm not even in the deadlift 400 range. But the idea of "maintain strength, improve conditioning" is a good one, if you're willing to dedicate six weeks to doing just that.
Ultimate Beastdom - Training to get "what constitutes strong"...strong Part 2
The Conditioning Block
I like how he's broken out his conditioning - time-based steady state cardio (Day 1, mile), interval aerobics with a strength element (Day 2, sledgehammer), round-based higher-resistance cardio (Day 3, hill running), and a steady-state deload (Day 4, 45-minute cardio). You get a natural progression as you run faster/swing the hammer for more rounds/run the hill more and then a deload to keep up some conditioning benefits but aid recovery. At the same time, the input varies - run a flat mile, run a short distance up a hill, swing a hammer.