Oooh - have never had a thread with my name in the title, how exciting! I'm not a super expert on linguistics - after doing a modern languages degree with some linguistics, I did a one year masters in linguistics, then went off and did a PhD in computer generated speech, so am much more of a speechy person than a language person.
Anyway - as a general, really fun book about language SenoraApostrophe's suggestion of Pinker's "The Language Instinct" can't be beaten in my view. The department I was in was very anti Pinker's theories in some ways, but he writes brilliantly and gives great examples that make you marvel at language. He does totally look like Simon Rattle too! And he wrote a great book on the Mind as well as the language one, but I digress.
Also can second the suggestions of books by David Crystal and Jean Aitchison.
If you're interested in SALT training it might be well worth contacting one of the places that offer a course and asking for an introductory reading list and then reading a few to see if you are still keen.
I'd have to dig around to find any more specific suggestions - it's so long since I read anything I can only remember the fun populist stuff now!