I'd also recommend the city park in Seward and the above link to the book "Alaskan Camping".
For Denali definitely stay in the park for the best experience and plan for an all-day bus tour. Do the school bus tour not the 'fancy' bus tour. The school bus is very low-key, the drivers are excellent at spotting the animals (even while driving), and they'll stop for photos. I think the 'fancy' bus tour gives you lunch though. :) Otherwise, pack your own.
For Fairbanks we stayed at Chena River Wayside State Rec Area right in town. Plan on doing the sternwheeler cruise.
For Homer we stayed at the city park on the Spit. It's basic but has the same awesome views that the more expensive parks have.
You didn't say how much time you have for the trip but plan for less days in Fairbanks than the other spots you've planned. Compared to the others, Fairbanks isn't that great but the sternwheeler cruise is very nice.
The Milepost is good for history and maps but not for campgrounds.
Purchase online the TourSaver 2/1 coupon book. One glacier cruise will pay for the book and there's one out of Seward. The sternwheeler cruise is also in the book.