| xl* | On-board Dell interfaces for newer machines, all newer 3COM 10/100 cards (including Fast Etherlink III) |
| fxp* | Intel 10/100 (Look here for info on weird fxp* behavior) |
| ep* | 3COM (10Mb) |
| ed* | ?? |
| vx* | older 3COM (including 3c905) |
Some info can be found in /usr/src/sys/i386/LINT.
Here's what I found in a table in /usr/src/i386/i386/userconfig.c:
ed "NE1000,NE2000,3C503,WD/SMC80xx Ethernet adapters" el "3C501 Ethernet adapter" ep "3C509 Ethernet adapter" ex "Intel EtherExpress Pro/10 Ethernet adapter" fxp "Intel EtherExpress Pro/100B Ethernet adapter" vx "3COM 3C590/3C595 Ethernet adapters" xl "3COM 3C90x/3C90xB/3C980 Ethernet adapters"