I am looking to get a tropical plant enclyclopedia where if a see a plant name written down i can just look it up, see a nice picture and the conditions they grow in.
Peter Hiscock's book has only small section on individual species. Most of the photos are emersed form. A waste of cash if you're only after plant info, IHMO.
Tropica's latest catalogue is excellent and describes in details all the plants on their site. Cost is £2.
The Big Dennerle Guide has a nice plant species selection in the back. £15.
Christel Kasselmann's book is regarded as the best for describing plants, but its the most expensive.
Peter Hiscock (what a name, huh! ), dated and some of the recommendations are just wrong (err towards way too much light, IMO).
Some bang for your buck, the Baensch series. Expensive, but the plant profiles are actually quite good, and the picture quality is good. Volume one covers the most common plants and details quite a few species. Volume 2 discusses the flowers and emersed growth for many more species and greatly expands on cryptocorynes and new species. Volume 3 updates cultivars and profiles non-aquatics. You also get both fish profiles and plant profiles in a handy book. The large species photo index for volumes 1-5 doesn't include plants I think, so you have to fork over the cash for the actual books, but boy, what an investment. It is presented in a field guide format and includes basic care and the scientific name. I love the Baensch books, great stuff, and if you know where to look, you can find good deals. Got my volume 2 for less than $5!