We've checked out a trial copy of a digital plant library called Horticopia here in the office - after all, not everyone here is a plant nerd and us real nerds have better things to do than answer questions and enjoy the sound of our own voices sounding smart all day.* It has all the info that you would expect from a quality plant encyclopedia, loads of pretty printable piccys and it can go everywhere with you on your laptop.
We would like to know if anyone in the landscaping or horticultural world has used the full product and which add ons of extra groups of plants they bought for it.
You can get a trial Horticopia CD for about £6 here: http://www.horticopia.com/
*Well, not many things.