I just got the Phil & Teds Sport. I consider it to be a "crossover" type stroller. Smaller than a jogger, but it has good size air-filled tires for off-roading. I don't think it's recommended for serious running, but it's supposed to be fine for a little jogging and the seat fully reclines, so it works for an infant.
I'm expecting my second in April and wanted something for walking on the trails and going to parks and races this summer (hubby is an amateur athlete). Since my son is 4, I didn't really want to get a full double jogger because he wants to walk sometimes, but obviously he can't do miles and miles and I need to have him contained when we're in a crowd.
The thing I liked about this stroller is the versatility. I am hoping it will replace my Graco travel system single stroller AND my single jogger when I have just the baby with me, either for a walk or at the mall. (There is an available attachment so you can snap in a car seat as well.) But what I thought would be really useful for me is the add-on seat so that it can be used as a double if needed. It's a little bit of an odd configuration -- stacked, as someone mentioned -- and I obviously haven't tried it yet, but it goes on easily and seems really sturdy. For me, my older will have to go in the main seat due to size, but I think with a smaller toddler you may have other options. Plus I figure my son will be a lot happier being able to see out and baby won't care for a while.