I've gotten bogged down lately in wrist devices - mostly the Vivosmart HR and the Forerunner 235. But there's a lot more to running gear than personal tech (shh, don't tell DC Rainmaker).
One piece of equipment I think of as a piece of running gear is the Cybex Lower Body Arc Trainer. This is the 750, but the current machine is the 770A.
The Arc trainer is my go-to on cross-training/non-running days where I want to give my feet a break from the pounding impact. Some research promoted by machine maker Precor seems to bear this out - that elliptical machines lead to significantly less ground impact than running but produce similar HR elevation.
For me, when using an HR monitor, I can pretty easily get my heart rate into running range by upping the resistance to 25-30 (default is 15) and keeping the cadence to a running-like rate (150+). And my feet, knees, and hips definitely thank me.
I also love the lower body Cybex because it is more "running-like". When you support your upper body on polls, you are doing less lower body work. And that is not helping your running. (Neither is leaning on the guard rails - you want to be activating your core muscles by supporting your own body, not letting the hand rails do the work of fighting gravity for you).
The Cybex folks seem to have put some thinking into the designs of the machine - they hired a phD to run their "Research Institute" who pondered issues of impact in this blog post.
I also use the arc as a supplemental workout when I don't feel like "doubling" up my running. And I particularly like it to do some intervals and to "get my steps in" -- I'm a compulsive step counter even more than I am a mile whore.