It's been said so often that it's almost a cliche, but it is nevertheless very true: "If you only have one grammar book, make sure it is Michael Swan's
Practical English Usage".
Despite his immense knowledge and usually perceptive analyses, however, I sometimes feel that he says things that are not quite true or that complicate matters unnecessarily, and he can at times sound a little prescriptive rather than entirely descriptive (that is, usages that he marks as wrong or ungrammatical can seem fine to me). I can't give you specific examples because I didnt take my copy with me the last time I left the UK! (I know that contradicts the advice in the very first sentence above, but I have bought this book FOUR TIMES over the years I've been abroad, and might well buy it again one day, so I feel I am familar enough with it to dish it a bit). Somehow managing without it though, because...
I don't have my nose stuck in just grammar books anymore - I now often prefer to check a dictionary instead (these have a lot of grammatical information in them, and reinforce and make very visible and obvious any grammatical "rules" - should be more "observations" I think! - through sheer force of example(s)).
So, I would strongly recommend you buy an advanced learner's dictionary (with accompanying CD-ROM) and install the CD-ROM onto your computer before you leave, or take the CD-ROM with you (if you don't have a computer and can't afford the luggage space/weight that the paper dictionary would take up). I wrote quite a detailed post about the general benefits of learner dictionaries for Dave's, the links are here:
http://www.eslcafe.com/forums/teacher/v ... php?t=1754
http://www.eslcafe.com/forums/teacher/v ... php?t=1734
Getting back to the grammar books, great though the Swan is (it's a joy to browse due to its very extensive index and cross references), it is in A-Z format, so it may be hard for you to get an "overall" view of English grammar or discern any authorial viewpoint regarding possible pedagogical implications. For these reasons, you might want to consider getting a more complete
grammar instead of a "grammar dictionary" like Swan's. Swan himself in the introductory matter of PEU recommends John Eastwood's
The Oxford Guide to English Grammar (it has a similar font and general feel to Swan, and should prove dependable for a teacher at any stage in their career; it is, in fact, probably my favourite grammar book at the moment. Do a search for "Eastwood" on the forums to find the other comments I've made about it).
The COBUILD
English Grammar is very good, but I don't think it provides quite the same "teacher-centred and friendly" guidance as the two above Oxford books...but you should definitely try to check it out.
There are more "detailed" grammatical descriptions of the language available (e.g. the corpus-based Longman grammars by Leech et al), and books covering "Systemic-Functional" approaches etc, but I would be wary of getting into stuff like that because it can start to assume you want to learn and adopt a particular grammatical metalanguage; certainly, there is a danger of terminological overload for little appreciable short-term gain, and just because you don't use a consistent metalanguage doesn't mean you are incapable of understanding the concepts
behind it at whatever isolated and pressing point in time, does it! If you really do want to get to grips with fancy terms, however, Sylvia Chalker and Edmund Weiner's
Oxford Dictionary of English Grammar is EXCELLENT and very affordable.
Tom MacArthur's
The Oxford Companion to the English Language is also well worth a look.
At the other extreme, there are the grammar practice books such as your Murphy's, and Azar's etc that are probably more for students than teachers. You will want to become familar with these simply because some of your students might be using them, or you want to set exercises for homework, but I don't think you should depend on them to inform your teaching much less your thinking too much (unless you really are pressed for time and need a "dummies' " overview quickly). I suppose they will show you what your average student should be expected to know after studying grammar explicitly, no more and no less.
Alternatives to Murphy's books would be the COBUILD
Student's Grammar (with exercises), or Swan and Walter's
How English Works (I prefer this to their lower-level
The Good Grammar Book).
Finally, a few books about grammar that go beyond the "What is grammar?" kind of questions you may be sick and tired of by now, and go some way to providing decent answers are:
Michael Lewis,
The English Verb. More loved than loathed by teachers, it seems, this really is a book that every teacher should read in the first few years of their careers. It's a slim volume, so consider packing it and saving it for (a) rainy day(s). (If you feel that Lewis is too discursive, Leech gets down to nitty-gritty intricacies in his
Meaning and the English Verb, Third Edition).
Celce-Murcia, M and Larsen-Freeman, D,
The Grammar Book, Second Edition. Some people on Dave's have knocked this, but I think it is a wonderful book, and a very affordable way to get an overview of how discourse factors affect grammatical choices. The only drawback is that it is big and heavy. An impressive, hefty tome.
Penny Ur,
Grammar Practice Activities. I've included this straight after
The Grammar Book because I think it demonstrates how superficial a lot of supposedly "communicative" activities can become when divorced from any serious analysis of real data (
The Grammar Book also has some duff activities in it, but at least it has analysis aplenty so you can start imagining better activities yourself. If you really must take an "activity" kind of book, at least make sure it's something like George Yule's
Explaining English Grammar, which kind of strikes a happy medium between the Ur and
The Grammar Book).
Lastly, one really nice, affordable book that could fulfil many roles for you, and may consequently be just what you're looking for, is Martin Parrott's
Grammar for English Language Teachers.
Scott Thornbury seems to be the "discovery" methods guru man nowadays (replacing Tomlinson and Bolitho, and Tony Lynch to my mind), and has attracted quite a following. I didn't have time to check out his
About Language, but I am sure it would be pretty interesting (if you like this kind of approach).