Besides my initial Web pages in Mt. Rainier National Park for day hikes and backcountry hikes guides - there are several other Websites with trail and hike guides, some with user reports, for western Washington (Cascade and Olympic Mountains). These can be expanded to focus specifically on Mt. Rainier NP.
The first is the newest, the Washington Trail Association (WTA) with access, trail information and user reports. It's an excellent resource.
The second is the Tacoma Tribune (newspaper) . It has excellent descriptions and information on the trails with Google map interface.
The third is Hiker (.org). This one is quite complete for information and maps.
The fourth is the Visit Rainier (.com) with excellent trail descriptions.
The last is the NPS guide to the trails in Mt. Rainier NP, along with the latest trail conditions.
Some of the trail and hike guides may not have the additional mileage of the Carbon River road which has been closed to vehicles at the NP boundary since November 2006. You have the check the information for the specific trail or hike. They either will have the mileage as noted after the November 2006 storm and flood damage, or they won't, which is an indicator it isn't included.
There are other on-line guides, and I welcome suggestions to add to this list. I haven't included commercial ones which require you to register and provide additional information. As this information is public knowledge and available in books and on Websites, I don't feel any Website should have prerequistes for obtaining information and descriptions or view maps, and therefore won't be included.
In addition these Websites are reasonably inclusive of many of the dayhikes in Mt. Rainier with considerable detailed information about the trail or hike or about their experience. These are excellent sources, but you have to use judge as to when they were there to assess the current condition of the trail and hike.