I play baseball too, and I ask a lot of professionals I know about weight lifting. They all pretty much agree to stay away from the low-rep workouts; they result in stronger muscles, but they are the slow-twitch type muscles that are detrimental to your game.
In baseball you don't really need big muscles--speed, explosiveness, and power are much more important than mass. Of course there are guys like Barry Bonds, Sammy Sosa, Big Mac, etc. who have HUGE muscles, but those guys are freaks and are on 'roids and have been working out for a VERY long time, so most of that huge muscle mass is fast-twitch fiber that has been built up over a long period of time.
Anyway, as an outfielder, speed is very important for you. You should spend a lot more time on the track and doing plyometrics and explosive weight training than you should doing slow-movement weight training.
Even as a hitter, there is a point where you can have too much mass, even if it is fast-twitch fiber. The best swings in baseball are all fluid, graceful swings (take Ken Griffey Jr., for example). Too much muscle will turn your swing into a cramped, tight, choppy swing, which is definitely not good.
Creatine and whey protein is pretty much a given these days, along with multivitamins (Centrum Performance!) and an extra dose of other vitamins. I couldn't really tell you how to take the creatine and protein though, because I just drink a meal-replacement shake called Muscle Milk that has all that in it.
I have a few baseball books that are very good:
52-Week Baseball Training by Gene Coleman (THE BEST BASEBALL WORKOUT BOOK EVER, this guy has worked with Nolan Ryan, Jeff Bagwell, Craig Biggio, Randy Johnson, Moises Alou, etc.)
High-Performance Sports Conditioning by Bill Foran Not as baseball-oriented as the previous book, but is much more scientific and detailed, and has a lot more exercises in it.
And some other books for sh!ts and giggles...
The Art of Hitting .300 by Charley Lau Awesome book with analyses of hundreds of hitters from early baseball to modern baseball. The analyses themselves are worth the buy, but it has a bunch of other stuff too.
Heads Up Baseball by Ken Ravizza and Tom Hanson I'm a personal friend and client of Tom Hanson, and he's the MAN when it comes to sports psychology. This book helps you get your head straight, your goals formulated, and helps you keep consistent and learn to play to your maximum potential. Highly, HIGHLY recommended for any sports player.
So there you go. Weight training is imperative for baseball these days, but make all your sets at least 8 reps, and try to modify the exercises to make them more explosive (for example, when I do benchpress, I do 4 sets of 10, and when I bring the bar down and push it back up, I explode as hard as I can--this is much more beneficial for basebal than slowly bringing it back up). And I would definitely stay away from Diesel's guide to bulking (for baseball). Hope this helps.
