If you make a lot of mortise and tenon joints, a Hollow Chisel Mortiser is a tool you should really consider. It makes quick work of the repetitive task of batching out mortises. And unlike the router, it leaves nice square ends that pair perfectly with tenons made at the table saw or cut by hand. This is a fairly comprehensive video and tells you pretty much everything you need to know to purchase, set up, and use a hollow chisel mortiser.
All tools and materials shown in the video are available via the links to the left.