I personally would buy the Haynes manual (or Clymer) - it'll cover most things.
As for spanner sizes, (I'm assuming you're just starting out) a normal 8mm - 19mm range of combination spanners (open at one end, with a ring on the other) will cover most things, a socket set covering those sizes is extremely useful too, and needn't be expensive. A 6 or 8 inch adjustable spanner comes in handy. Other useful items are screwdrivers, feeler gauges, and an oil filter wrench. If you plan on doing electrical work (some people just don't like touching electrical jobs), get a multimeter (basic digital ones can be had from a fiver or so). Also, get some Allen keys.
As you become more accustomed to doing your own jobs, you'll have a better idea of what tools you want / need - its easy to buy tools you don't really need and which never get used.
Halfords is usually a good bet, as are motor factors. Final point: stay away from the *very* cheap crap (buy cheap, buy twice) - half-decent stuff isn't usually cheap (although it needn't be bank-breaking expensive either), but will last longer.