I've heard a lot of talk in the ancient history forums infrequent about Alexander the Great's pikemen, and nobody seems to agree as to their effectiveness in combat, and who the pikemen were deployed against in combat. As best I can tell, they were some of the most dangerous infantry units in the ancient world, and very hard to kill with missile weapons. But some people in the SCA I know saw that they were meant as the anvil in a hammer-and-anvil tactic, with his cavalry being the hammer. The reenactors on RomanArmyTalk.net say that there is not a single reference in any original source(including all the years after Alexander that pikemen were used) as to the cavalry ever engaging infantry. Could someone clear this up? Or do we just not know enough? Thanks!
Alexander's infantry was a diverse body of which sarissa-wielding phalangites were just one part. Alexander's tactics generally did not follow the "hammer-and-anvil" pattern. We have pretty decent descriptions of several major battles from Arrian, who had access to several first-person and secondhand accounts of Alexander's generals and fairly extensive campaign journals.
Cavalry was mostly employed as a screening measure, as a stopgap when the enemy had posted ambuscades, as a high-mobility group that could change position to provide aid, and, as used in many classical deployments, as a counter to enemy cavalry and chariots. The cavalry arm was also used in flank attacks (the "roll-up") after the infantry had engaged and to run down routed infantry. They were infrequently (I would say "never" as I do not recall any references in Arrian, but that would be too cocksure) used to drive infantry forward onto the phalanx.
Alexander's tactics could best be described as versatile and sometimes novel. He deployed a variety of troops -- phalanx, heavy and light infantry, archers, peltasts, heavy and light cavalry, etc. in many different ways to best suit the terrain and the enemy disposition. He generally used an oblique formation to destabilize linear enemy lines, sometimes referred to as "pivoting". His tactics were often unconventional, as at Gaugamela where he faced a numerically superior force and won.
The phalanx's best strength was its pressure, much like the Greek hoplite formation. The Macedonian phalanx was invented by Alexander's father, Philip II, who took a battered, war-torn nation and militarized it in a few years. The "bristling pikes" of the formation proved to be an effective "steamroller" against even the heaviest infantry of the day. It won decisively against the hoplites of allied Greek states including Thebes and Athens early on, but was (sadly for some historians) never and was successfully tested against the Spartans.
I recommend reading Arrian as well as Pietrykowski's "Great Battles of the Hellenistic World". The former is an entertaining and informative read, and while the writing of the latter can often be redundant and poor, I found the visual aids and descriptions of tactics and battle deployment, as well as background information on Philip II and his military reform plan, informative.