[Gandalf Parker]

vinemen can really supplement an army early in the game. They dont eat, and they have high morale. Vine Ogres can be even better.

Wyverns can be handy as a flanker. Set them far to the sides of the combat (the top and bottom of the formation screen). You can have it attack archers immeadiately or set to hold-and-attack rearmost. I generally find that having my archer-attackers at the top of the screen and my attack-rearmost flankers at the bottom seems to work best against the usual AI setup.

The spell "awaken sleeper" can give you a great commander at a time when you might really need him. He leads alot of troops, of any type (including magical and undead). He has good hitpoints, strength, just about any stat. I like to give him the Thunder Bow because it specifically uses his strength.

Generally, the summons need to be used for their best attributes, not as replacements for regular troops. The stealthy ones are great to add to a stealthy army, the fliers can help add some variety to flying armies or other places that you need fliers, the mages can be very useful to fill in magic areas you dont get otherwise, and the ones that can be dropped into provinces you dont own yet are great for suddenly taking areas that you find the enemy has weekly defended.