Talk to any IT services companies about Green IT and most of them will try and sell you virtualisation products for your server farms and thin clients for your desktop estate.
This approach will only meet some of your objectives, now is the time to develop a long term sustainable Green IT strategy based not only on technology but also in educating your IT staff and users into thinking smarter.
Carbon3IT Ltd are developing a holistic Sustainable Green IT programme based on the BCS 5 step plan that will assist your company in designing and building a sustainable computing IT platform that will be cost effective and socially responsible.
http://www.bcs.org/upload/pdf/sqm2009-raisingawareness.pdf
All Carbon3 IT Ltd consultants have attained the Foundation Certificate in Green IT and will take the other courses mentioned in the link when they are available.