PPPoE: point to point protocol over Ethernet
According to dslreports.com, DSL providers are increasingly moving toward PPPoE to deal with IP address shortages and better integrate DSL customers with their dialup recordkeeping systems. Theoretically, one could have multiple service providers through PPP over a DSL line. (For more details see http://www.dslreports.com/information/kb/PPPoE).
In my experience setting up PPPoE is a bit of a bother, but bandwidth is just as high as a standard DHCP DSL connection all other things being equal. One can usually set the PPPoE client to start automatically on startup, preserving the "instant-on" illusion.
PPPoE clients are available for Windows, Mac OS and Linux operating systems, among others. BeOS is one OS that does not currently have a client, but the Linksys Etherfast 4-port Cable/DSL Router (or its one-port variety, or a competing product) is PPPoE compatible, and acts as a DHCP server to BeOS' DHCP client.