I believe I read a Malmo post where he said something like "grasshopper not chase run. Let run come to grasshopper" That's actually good advice. I think you may be stressing a little too much about your pace on the long runs. Just let it happen. Some days you'll feel good & run faster than others, but if you run 8:00+ on a long run, don't sweat that at all.
Other things to try:
Progression runs - these should be longer than tempos, but shorter than long runs. You may just want to let these happen as well. Your medium-long runs will sometimes just turn into a progression run
Hill Sprints - 8-12 second bursts up steep hills. I'd recommend these over 'hill intervals' of longer duration - at least at this point of the season
Cruise intervals - basiclaly just breaking up a tempo or threshold run into pieces with short recoveries.
Form drills - we do these when we do strides. Google Pete Magill. He has a good, free video on technique drills
General strength/mobility exercises - Google Jay Johnson's series on these. Great, free videos.