I first discovered Raven et al.'s Biology of plants (hereafter referred to as BoP) in its 6th edition, published in 1999, when designing a second-year undergraduate ‘botany’ course. Whether it was because this was the first book I'd secured as a free ‘Instructor evaluation copy’ of a textbook (one of the few ‘perks’ of being a university lecturer … ), I can't be sure, but it's been a constant companion, and on my recommended reading list for my plant biology courses (with suitable updating to 2005's 7th edition), ever since. Why? Because it was – and still is! – a great, all-purpose, general plant biology (botany in all but name) text, which includes abundant coloured diagrams, photos and photomicrographs, a substantial glossary (26 two-columned pages), a comprehensive index (64 three-columned pages!), suggestions of further reading (many of which are dated post-2005 as befits this ‘most significant revision in its history’) by chapter, a highly readable – therefore pedagogic? – style, and covers all the basics, from evolution, taxonomic overview of Kingdom Plantae (plus bacteria, archaea, viruses, fungi and algae), ultrastructure, anatomy, physiology and biochemistry, ecology (although those latter two chapters are now only available online), and even plant–people relationships (both as a separate 22-page chapter and as 15 short essays throughout the book's approx. 900 pages). Along with the extensive updating, Peter Raven's name has disappeared from the listing of authors. It is not clear to me why this has happened, but this 8th edition is dedicated to the much-lauded gentleman (a Time magazine ‘Hero for the Planet’; http://en.wikipedia.org/wiki/Peter_H._Raven) and who is now honoured in BoP's updated title, Raven Biology of Plants. And BoP retains its distinctive impressionistic cover – van Gogh's 1890 ‘Field of Poppies’ this time – which makes it stand out from the other books on the shelf!
Does such a wonderful book have any competitors? Yes, there is a big, competitive market for undergraduate textbooks and plant biology is no exception. However, the textbook closest in style and coverage to BoP – that I know of – is the approx. 700-page tome Mauseth's Botany (2014), now in its 5th edition. I like ‘Mauseth’ (and it's not just because it's entitled botany!), but tend to turn to BoP first and supplement information from that source with material from other texts – such as Mauseth's. And you will need to supplement BoP with other sources. If you want more on the plant physiology side of things, then you will probably need the likes of specialist texts such as Taiz and Zeiger (2010). If you are after more of the molecular biology dimension, then Smith et al. (2010) or Jones et al. (2013) will help. To delve deeper into the structural–developmental side of plants, texts like Beck (2010) will be needed. For more on those all-important plants-and-people aspects of botany, then invaluable are Levetin and McMahon (2012) and Mauseth (2013), etc. The point is not that you don't need any other text than BoP, because you do!, but BoP is an excellent starting point for the basics of plant biology. Simply ‘mix-and-match’ BoP with your favourite, more specialist other texts to get the desired final outcome as suits your particular audience.
So, in concluison, I don't think you can beat Raven Biology of Plants as a great all-round, comprehensive introduction to botany (oh, alright then! plant biology).
An aside: the above comments refer to the so-called International Edition – ‘for use outside the USA and Canada’ – of BoP, 8th edition. I've often wondered what may be different in this edition compared to the USA one, and scrutinising Amazon's UK site I think I may have found the answer. The non-International Edition is shown retailing at about £120, but a reviewer (http://amzn.to/1jxOoOa) says that both editions have the same content. So, maybe the International Edition should be renamed the ‘Austerity’ Edition. In any event, it is nice to know that the Americans are helping out the cash-strapped botany students of Europe and non-USA/Canada!