Just asking, how are you under a 1000 if your turn based is over 1600?
Help me choose best tactics book please

best is Tactics Trainer of course :) ...
+1 and there are a lot of other tools on chess.com
Chess mentor an computer workout have enough material to keep you busy for a long time.

All the suggestions you get so far are all fantastic, read them all if you have time.
When you reach approx 1800-1900, do consider :-
1. Anthology of chess combinations
2. Perfect your chess

303 tricky chess tactics by Bruce Albertson is probably best for you. I know Ive gone over that book many times and my tactics trainer is in the 2550-2670 range.

1001 Checkmates and 1000 Winning Chess Sacs + Combinations by Fred Reinfeld are cheap (used PBs) and available. The Polgar book is supposed to be great, and it's pretty cheap too (used PB). I prefer books with "brand name" recognition, even though a lot of players may turn their noses up at anything by Reinfeld; but I suppose there are plenty of good chess books by writers who are not IMs or GMs (Reinfeld wasn't).
All 3 I mentioned are available at amazon right now, just search for the authors name there. I'd go with Polgar's book because of the price and reputation, if I didn't already have dozens of other unread chess books lining my shelves :( With 5334 Combos & Games you probably won't need any other combo or tactic books for awhile!

1001 Checkmates and 1000 Winning Chess Sacs + Combinations by Fred Reinfeld are cheap (used PBs) and available. The Polgar book is supposed to be great, and it's pretty cheap too (used PB). I prefer books with "brand name" recognition, even though a lot of players may turn their noses up at anything by Reinfeld; but I suppose there are plenty of good chess books by writers who are not IMs or GMs (Reinfeld wasn't).
All 3 I mentioned are available at amazon right now, just search for the authors name there. I'd go with Polgar's book because of the price and reputation, if I didn't already have dozens of other unread chess books lining my shelves :( With 5334 Combos & Games you probably won't need any other combo or tactic books for awhile!
I forgot about that book....that one is GREAT!
Best high-level tactics book I know: "Modern Chess Tactics" by Ludek Pachman. For lower-level players I like Fred Reinfeld's old "Complete Chess Course." In my day I cut my teeth on its original constituent 8 volumes. Also, even older but good is Siegbert Tarrasch's "The Game of Chess."

Chess Tactics by Paul Littlewood is a lovely little book, well structured,
it organises chapters by motif, gives examples of the motif, then a number of positions for the reader to solve using that motif.
e.g. chapter 1 PINS
a pin is defined, simple examples of a pin are given, examples of exploiting a pin, then problems to solve (ten of them).
chapter 2 is skewers and so on
a nice book that is usually pretty cheap on Abebooks.com

Chess tactics is by JOHN Littlewood, not PAUL. I am surprised to see that it is out of print. Ditto the recommendation. As the poster above says, get it from abebooks.co.uk (or .com). The prices quoted on Amazon are excessive.

http://www.chesstactics.org/index.php?Type=toc&Expand=21
It's free. It's perfect for beginning players, and it's really good.

Gavinw, you are right and I am wrong. I am sorry. I was confusing the tactics book with "How to play the middle game in chess", which is definitely by John not Paul. Rather silly of me. Paul's tactics book is the one I had in mind when I ditto'd the recommendation.
The Complete Chess Workout, by IM R. Palliser. Guaranteed improvement. 10 tactics/day keep the blunders away!