The whole stretch of Cascade Lakes Highway grants you access to all sorts of beautiful areas. Mountains include Mt Bachelor, Broken Top, the Three Sisters and more. All the lakes up there have their unique aspects, but my personal favorites are Devil's Lake for it's wonderful turquoise color, and the meadows of Sparks Lake. Those are both roadside attractions. If you're up for some hiking, Green Lakes and Moraine Lakes offer some great mountain backdrops. Word of warning: bring bug spray of some sort if you're visiting these lakes. The mosquitoes in July can be soooo bad.
For night time stuff, I'd still consider the Cascade Lakes Highway to be the best access point for that. The only light pollution you get out there will come from individual campers or resorts (if you get close enough). But it's easy to find an empty meadow with no man made lights in view to get some night shots.
Some other places I recommend that aren't in the immediate area are Smith Rocks State Park, and Newberry Caldera. The latter has a trail that takes you past some nice waterfalls (although not very large), and up to a couple really nice lakes and vistas of the surrounding areas. The former is pretty dramatic looking, and has a river running through that makes for the perfect refreshing dip in July.
A fantastic waterfall is Tumalo Falls, but as of now it's off limits due to some restoration work (I think). I'm not sure when it will re-open, but if it does, I'd try to make it out there. If you'd like to get a level view of Mt Bachelor for a shot, hike up Tumalo Mountain, which is directly across the road and gives the perfect vantage point.