I regularly employ the use of biodiversity data like SEINet to crossref with herbarium specimens. Honorable mention to the North American Ethnobotany Database for pulling up bibliographic info on plant-human interactions. There's also a tool to lookup collection site IDs for cacti and succulents here: BCSS Field No. Lookup. These aren't necessarily in the realm of plant care but I believe they could make a nice additon to the sidebar. Cheers!