The later in July you come, the more trails will be open. The Falcon Guides book by Eric Molvar is a good start.
With the Highline Trail, you can start early (really early, 7:00 or so), leave a car at the Loop, take the shuttle to Logan Pass, and you can hike down from Granite Park Chalet to your car. Otherwise, you can hire a shuttle to St. Mary from Many Glacier, and then you can take the free park shuttle to Logan Pass.
Some of my other favorite dayhikes include:
Siyeh Pass (leave a car at Sunrift Gorge, take the shuttle to Siyeh Bend)
Ptarmigan Tunnel/Iceberg Lake (do them together)
Dawson-Pitamakan (a true loop, though I prefer to do it Pitamakan Dawson, counterclockwise)
If you can, though, getting into Glacier's backcountry is worth it, even if only for a night. If you have time, put in a permit request by April 15, and you can make the lottery. If not, there is still plenty of walk-in options, but you'll have to be flexible.
If you want PM me, and I can give you more details. Have a great trip. Glacier is an amazing place.