Resources:

Arabidopsis resources:  We use Arabidopsis quite often as a model organism.  The Arabidopsis Information Resource (TAIR) is a great repository of Arabidopsis genomic information.  Additionally, you can check out the SALK Institute SIGnAL website to identify T-DNA mutations or cDNA clones for your favorite gene.  This primer design tool is useful for quick T-DNA primer design.