The last time I had that problem there was three things the tech checked for in addition to the ignitor.
1 - Sail switch, this is located inside the cover for the fan. When the fan gets up to speed it will move and turn the switch on to allow the furnace to ignite.
2- Overheat switch, this is located under the heat exchange. If it gets too hot this switch will turn the furnace off. Can malfunction and cause the furnace not to come on.
3- Computer card, this can go bad and cause intermittent problems with the furnace not comming on.
My problem turned out to be the computer.