Lots of great day hikes (all distances round trip)
Out of Many Glacier:
Iceberg Lake (10m) - easy, not too much elevation gain, usually lots of critters (huckleberry fields tend to draw bear; moose common near the lake)
Ptarmigan Tunnel (10m) - a lot of uphill, stunning views up into the Belly River drainage when you get thru the tunnel
Grinnell Glacier (12m) - easy, great way to see Grinnell Glacier (do it while you can; may not be around much longer); you can cut a few miles of flat, forest hiking off the trip if you take the boat
Out of Two Medicine:
Oldman Lake/Pitamakan Pass (15m) - easy 'till you climb the Pass, but that's not too bad and the views up there are awesome (if you continue up to Dawson Pass, you can loop back to Two Medicine along the lake; adds 3m but adds even more amazing scenery, and you don't have to retrace steps- we were going to do that 3 weeks ago but were driven off the Pass by a nasty storm); great wild flowers on this hike, although the beargrass will be done by the time you get there
Out of Logan Pass:
Haystack Butte (6.5m) - nice hike along the Highline/Garden Wall, great chance to see goats, bighorn
Granite Chalet/Grinnell overlook (16m) - extension of the Haystack hike, pretty cool to see the Chalet; the overlook is all uphill (.9m one-way) and a bit of a slog, but absolutely worth it to see the Glacier from above; bear not uncommon, especially near Granite (we saw mother grizz and 2 Cubs in the meadow below the trail last week); you can cut 3 mile off the trip by taking the Loop Trail but that's all downhill, exposed (due to the 2003 fires), hot as hell, and not all that interesting
Hidden Lake (6.5m) - easy hike down to the lake; coming back it's a 900' gain to get back to the trail; lots of goats, usually, along the trail, bear not uncommon; friends of ours spotted a wolverine up there last year
Piegan Pass (9m) - uphill, but a pretty gentile climb and the views up at the pass are worth it; actually, it's about a mile east of Logan Pass on Going-to-the-Sun highway at Siyeh Bend
Out of Avalanche:
Avalanche Lake (5m) - hike is mostly thru trees, including a neat old-growth cedar forest at the start; if there's any water left up high, the waterfalls into the lake are pretty cool
Out of Bowman Lake:
Numa Ridge Lookout (10m) - first mile is relatively flat along the lake, then it's all uphill and the last few switchbacks to the Lookout are a real slog but the views are spectacular; bear not uncommon, watch your packs at the top - the ground squirrels are very aggressive. Btw, the road up from Polebridge sucks big time
Out of St. Mary:
St. Mary/Virginia Falls - easy hike, cool waterfalls; lots of burn from the 2015 fires
Camping - some nice campgrounds in the park that fill up quickly (check the Parks site for fill times to get an idea); most are basic, with water and bathrooms but no utilities, no showers except for Fish Creek, St. Mary, and Many Glacier
Many Glacier has put about half their sites on reservation; if you want a walk-up, be in line at 5AM (no kidding); showers available at Swiftcurrent Motor Lodge
Glacier is ramping up their (free) shuttle system and it's a good way to get around the park. Over the past couple years, crowds have gone way up and it's getting more difficult to park at places like Logan Pass (lot was full at 8AM the other day), Avalanche, etc. The shuttle does not run to Two Medicine, Cut Bank, Bowman or Kintla; there is a shuttle to Many Glacier but you have to pay. At some point, I expect them to go to all-shuttle, like Zion, to cut down on traffic in the park; where they're going to build parking lots for all the visitors is a mystery.
I hope you realize that Glacier will not be the best place to get the full effect of the eclipse, since it's about 500 miles north of the band of totality. We're heading south out of Whitefish a few days before to visit friends in Three Forks (may push a little farther down, depending on what traffic looks like). If you can't get south, I'd drive east out on to the plains on the Blackfeet Reservation, and watch it from there.
Also, it has been a very hot, dry summer and fire threat is very high; be flexible and keep checking Inciweb. We've been lucky so far, but that could change any minute; right now we're just getting smoke (from fires down towards Missoula).
Have fun, check the expiration date on your bear spray (no kidding).
A few pics from the Granite/Grinnell hike we took Saturday
Grinnell Glacier (.9 miles up from the trail; bitch of a hike but worth it)
All my other pics from Glacier are on PeeBucket; can't display them until I migrate some of them to Flikr