Resources for locating campgrounds

As many of you know by now we will be visiting Overland Expo in AZ in May. However, we are not going directly there, we are flying into Denver a week before, then flying out a week after, and in between travelling in a small class B camper van.

Of course, we camp a lot in Europe in our truck camper; I have driven many miles in the US; but strangely to date we have never camped in the US :R.

So I need some help when it comes to locating campgrounds. My GPS shows campgrounds near our route, but on investigating on the internet many appear to cater to those who want to turn up in a 40ft coach and park up for 3 months.

As a couple in our 40s without children and who like nature we are looking more for campgrounds (whether commercial or national park) with the following features:

1) Scenic.
2) Quiet.
3) Just staying 1 night at each location.
4) Somewhere we don't have to book - i.e. we can just turn up one evening in May.
5) Electric hook-up would be nice.
6) Ideally somewhere nearby we can fill up with water / dump tanks.
7) Ideally a shower / toilet block nearby

5,6 and 7 are nice to haves, but not necessary everywhere.

Because this is a compact vehicle (E-series van) then some boondocking might be possible (e.g. on forestry land, I don't mean Walmart), but I wouldn't know where we could do that.

So, are there any good resources for searching for campgrounds that match the above criteria? E.g. websites, books.

The rough route we will take will be from Denver South past Great Sand Dunes to White sands, West to Tucson, then North to Expo near Flagstaff, then returning North East via Mesa Verde and maybe Rocky Mountain NP. So if anyone has any specific recommendations on that route they would be most appreciated.

Thanks in advance guys,

Steve.