Jogging ... my favourite route is from St Hugh's to Godstow (along roads), then back through Port Meadow ... Port Meadow is a fantastically beautiful place to jog (lots of open space with the river and the canal to one side), though a bit of a trek from Hilda's (it's to the west and north of Jericho, in North Oxford).
A lot of people jog in University Parks (next to the science site, close to Keble, tis nice and flat with wide paths). As in, a lot a lot ... personally it puts me off, but you can always leave Parks and head off in Marston direction. Closes at dusk though. Another good park to jog in is South Parks (google it ... close-ish to Hilda's), has a massive hill, which might be a good or a bad thing (good for fartlek), but very satisfying - fantastic view of the 'dreaming spires' from the top.
Lots of people jog in Christchurch Meadows (near Christchurch (!) and Merton, so Hilda's end of town). I suppose you could jog along the river at quite a lot of points, though towpath at night is not a good plan.