The Longmire Museum is small but worth visiting. It has an impressive taxidermy collection, from bygone days when it was considered appropriate to respond to seeing a marmot, fox, owl, or cougar by shooting and stuffing them.

"Sunrise to Paradise: The Story of Mount Rainier National Park", by Ruth Kirk, covers the geology, biology, history, and sociology of the mountain. Great information about how Native people used the area before white settlers arrived, and the gradual evolution of thinking around what the purpose of a National Park should be. Also, many wonderful photos.

"A Year in Paradise", by Floyd Schmoe, is a firsthand account beginning in 1920 with a young couple caretaking the Paradise Inn while buried under deep snow. It follows the changes brought by the arrival of spring and a career shift to work as a mountain guide, and ends with Floyd taking his wife and young son around the Wonderland Trail on horseback (using the same horse that had carried supplies up to build the guide hut at Camp Muir, no less). Vivid descriptions overflow with loving observations of plants and animals, from someone who went on to become a Park Ranger and then the Park's first official Naturalist.

The Mountaineer, volume 8 is a fascinating historical record of the first ever circuit of the Wonderland Trail, by The Mountaineers in 1915.

Park brochure from 1919 includes a map that shows trails notably different from those of today. Sunrise did not yet exist, and the Wonderland went via St. Elmo Pass and part of what is now the Westside Road.

Roadside Geology of Mount Rainier National Park describes the fire, ice, and floods that created this landscape.

An Administrative History of Mount Rainier National Park details (in arguably a bit TOO much detail :-) the politics of how the park was developed and policies changed over time. I find it interesting to consider how different this mountain could be today, had these past decisions gone in different directions.

Mining Glacier Basin covers Rainier's history of failed mining efforts.

Soo Too Lick: Indian Henry and the Mashel Prairie documents the life of the namesake of Indian Henry's Hunting Grounds and Satulick Mountain.

Cowlitz Connection is a video of two Taidnapam elders talking about Ohanapecosh: "You're in a very old, old sacred place of ours, where the people would come and they would do the work on themselves, to heal themselves. [...] And you coming here, you're a part of it here by just your mere presence. It's a really good thing."

Resources

Mount Rainier Recreational Forecast - my favorite source of weather info.

Road Status - expected opening and closure dates, important during the off-season.

Trails and Backcountry Camp Conditions - info from the Park Service.

Rainier webcams - check current weather and snowpack level for yourself.

Washington Trails Association trip reports - learn from recent experiences of others.

Northwest Avalanche Center - invaluable forecasts for deciding which days to snowshoe vs. stay home during winter.

Wonderland Trail Facebook group - members-only discussion group, very helpful for any Rainier questions (not limited to only those hiking the full Wonderland).

Wonderland Guides - great (albeit slightly stale) info about Wonderland camp selection, permit process, food caching etc.

The Ten Essentials, Hiking Etiquette, and Leave No Trace - things every hiker should know.