Phylogenetics
TreeBASE - A centralized location for a vast scope of phylogenetic information.
Tree of Life - A searchable, clickable cladogram with information about every form of life on earth.
Melastomataceae.net - This is a portal into the GBIF, and other, taxonomic databases

Herbaria & Collections
Types - Search the Smithsonian (US) collection of nearly 2000 melastome type specimens.
Collection - Search the entire collection at the New York Botanical Garden (NY).
Types - Type specimens at the New York Botanical Garden (NY).
Types - Type and general specimens at the Harvard University Herbaria (HUH).
Types - Type specimens at the University of Florida herbarium (FLAS).
Paris- Search the Museum National d'Histoire Naturelle (P).
Collection - A directory of genera, species, and collection label data for Melastomataceae in the collection at the Instituto Nacional de Biodiversidad (INBio), Costa Rica.
Illustrations - An excellent set of illustrations from the Smithsonian Institution.

DNA
NCBI - Search GenBank for DNA sequences of melastomes.
IPCN - Index to Plant Chromosome Numbers.

Taxonomy resources
Synonymy - This is a complete but short list of synonyms at the family level.
Genera - A list of all currently accepted genera (with synonyms).
IPNI - The ultimate in plant names and bibliographic references.
Kew Bibliographic Databases - This is an important resource for conducting literature searches.
Brahms - This is an excellent database that anyone may use for botanical investigations or collections management.

Floristics
Rhexia and Tetrazygia in Florida - Info and images from the Atlas of Vascular Plants of Florida
Melastomes in the U.S.A. - Most records pertain to Puerto Rico.
Miconia in Sao Paolo, Brazil - A database of Miconia species including photos and descriptions.
Flora of the Cerrado, Sao Paolo, Brazil - A search of this database from the Base de Dados Tropical yields species along with nice photos.
Central French Guiana - A collections database of Melastomataceae from NYBG.
Acre, Brazil - This collections database is part of a NYBG floristics and economic botany project.
Images - A collection of images of melastomes from Tropicos; many are type specimens.
Flora of Thailand - Information specifically pertaining to that project, the vegetation, and botanical investigations in Thailand.

Conservation
Rare plants - Search the World Conservation Monitoring Center (part of the IUCN) for threatened species.
Rare trees - Similar to the previous link, this one provides data only on tree species.

Miscellaneous
Charles Darwin - Did you know that even Darwin himself was driven nearly to madness by melastomes? Go to this page, hit ctrl + f and type 'mela' in the find box to get to the right paragraph quickly.