Pike and spear+shield builds definitely work, and long polearms are still the #1 cavalry deterrence.
For a pikeman-build you can always use a Shortened Spear or Quarter Staff (one slot) as second weapon so you can go 100% polearm wpf. Not fantastic weapons, but decent enough for self defense in tight situations. Other option is to carry a fairly light shield (2-3 shield skill) on your back to reduce projectile damage from behind.
Spear + shield is pretty fun to play in my opinion. I've got a money-earner-outfit on Ildov (who otherwise use the bec and quite heavy mail) which is Padded Armor, Heater Shield, and Spear, and it works really well as a support-fighter, and if you have to fight alone you can always put the shield on the back to get four attack directions, instead of only thrust. It's excellent to be a hard-to-touch fighter, that at the same time can mess with shielders and give annoying pokes to pretty much anyone while besting their range.
For a more serious shield+spear build you have the Red Tassel Spear, War Spear, and the Awlpikes. The Awlpikes however can't do side swings as far as I know, but have excellent reach and thrust damage.