There are no perfect web viewers for ecological and public land GIS.
ProtectedPlanet is an open-source platform that has the most comprehensive map of special protected areas for the whole world. In the US, highlights include BLM Areas of Critical Environmental Concern (ACEC), USFS Research Natural Areas, Special Botanical Areas, etc.
Peakbagger.com has the best index of free online topo maps, and their database is searchable for mountain ranges and peaks (Google often can't find geographic features).
SEINet is fast becoming the most comprehensive botanical specimen map database in the world, with new collections constantly expanding their coverage.
Wundermap has many useful features, including a better display of, for example, USGS's Stream Gauge Network, as well as weather and sea surface temperature.
I'm still trying to decide if the Forest Service's ForWarn system, or their Disturbance Mapper, is a better way to view forest fire, insect infestation, and phenology data. Both are slow and clunky as of this writing.