Probably beyond that would be the NE2000 network board which is very well supported both Amiga and DOS platforms. I doubt its relatively easy though...
The most obvious would perhaps be to mimic the PCMCIA slot of the A600 and A1200, with an NE2000 card yes. I'm not sure where on the chipset the PCMCIA slot is implemented, but with A600 and A1200 also both having IDE, and both IDE and PCMCIA being "ISA bus", I am guessing .... Gayle?
Other slightly obvious alternative (which I believe Chaos briefly started on for MiST), is a zorro2 ethernet card that was supposed to be used with e D-Link DUB-E100 USB dongle - on the MiSTer I would prefer to go via Linux (and hence also wifi) rather than needing a usb ethernet dongle though
Third option, mimic the A1200 clock-port, for which there are/were several high speed serial port interfaces, such as the Silver Surfer etc. There are also clock-ports for other Amiga systems, on various Zorro cards and A600 extension cards. Depending on where the clock-port is implemented, the drivers may need adjusting for the different address space on the various implementations.
Fourth and perhaps best option, is to not emulate any particular existing hardware, but instead make a direct connection to a dedicated device on the Linux side, and just focus on keeping it simple and fast, and then find someone who can write a sana2 driver for Amiga. With all the SPI ethernet device drivers popping up these days, I don't think it would be so hard
I suppose option 3 and 4 above are essentially the same - a relevant thread for info... http://eab.abime.net/showthread.php?t=91820
Instead of having a sana2 driver that speaks with ENC28J60, have a sana2 driver that speaks with the device node on the Linux side.
Oh, then there is the parallel port, in which people these days often use a Plipbox (http://lallafa.de/blog/amiga-projects/plipbox/
) and then I can just as well mention Amiga-Link, which was a networking device that plugged into the floppy drive port (http://www.bigbookofamigahardware.com/b ... px?id=1798
), I have a couple of those