Arbnet.org  http://arbnet.org
Great website sponsored and coordinated by The Morton Arboretum in Lisle, IL.

ArboretumWalk.com   http://arboretumwalk.com
Website with blog and reviews of specific arboreta.

BotanicWalk.com   http://botanicwalk.com
Botanic Garden website

The Arnold Arboretum     http://arboretum.harvard.edu
Website very focused on science, lectures, and access to one of the oldest research libraries in the country.

National Bonsai and Penjing Museum at the US National Arboretum. Washington DC

United States National Arboretum  http://usna.usda.gov
Website focused on the National Arboretum in Washington DC.  Location of the National Bonsai Foundation office, the National Bonsai and Penjing Museum, and the National Capitol Columns.

Job Search in horticulture     http://hortjobs.com
Great site with listing of jobs specializing in horticulture.

Wikipedia.  Listing of Arboreta in the United States.

Jobs for arborists on Indeed.com

Arbor Day Foundation.  http://arborday.org
A "must join" organization for anyone interested in tree protection and reforestation projects.  This website is full of valuable information.

APGA       American Public Gardens Association.    http://www.publicgardens.org
Website with listing of public gardens and job search.  Good for general information.

New England Bonsai   Bellingham, MA  http://nebonsai.com