ARABIDOPSIS

MATDB  - searchable index and visualization of positional information for BAC clones and single genes
TIGR Arabidopsis Database
Arabidopsis Functional Genomics Consortium (AFGC) 
Plant Plasma Membrane Database (PPMdb) - Arabidopsis plasma membrane proteins with expression and sequence data
Arabidopsis Genomics, TAIR
Plant Plasma Membrane Database (PPMdb) - A. thaliana plasma membrane proteins with expression and sequence data 
AtDB (TAIR)- genetic/physical mapping data
Arabidopsis thaliana chromosomes 4 & 5 - genetic/physical maps 
The Arabidopsis Information Resource
Arabidopsis cDNA Sequence Analysis Project
The Arabidopsis Genome Center (ATGC)
Everything Arabidopsis
The TIGR Arabidopsis Database Project

COTTON

Cotton Genome Center at U. C. Davis
CottonDB - a genome database for Gossypium

MAIZE

MaizeGDB 
Maize links  (Maize Co-op at the University of Missouri)

RICE

Rice Genome Database (Beijing Genomics Institute)
Rice Genome Project (Syngenta)
TIGR Rice Annotation and Informatics
Rice Genome Research Program

SORGHAM

Comparative Grass Genomics Center - University of Georgia
Sorghum Genomics Project - Texas A & M
Sorghum DB Data Collection Site