I bought my furnace from AC wholesalers and had it installed by a company. Wayyyy cheaper, however you may call a couple places ahead of time as some installers wont install equipment they dont sell you directly.
That being said, the furnace came within a week from a freight delivery company, they called ahead of time to set up a time for the delivery guy to unload it, worked great, wasn't damaged or anything.
EDIT: It also came with a 10-year warranty although I can't speak to how much of a pain it may be to actually exercise the warranty, or if it had come damaged...