If you're running either on roads/sidewalks or on trails that are visible from aerial photography, you can plot your course very accurately on mapmyrun.com .

Then a simple stopwatch can give you the rest of what you need to know. The timers in most phones have lap capability, if you have a way to make your phone's screen accessible when you run. If you have a smartphone, there's an iMapMy app that uses your phone's GPS - the free app is all I've used, and it worked quite well (aside from issues of simply being able to access the phone), but there are pay options as well.