A lot of native Amiga screenmodes have a 15kHz scan rate, so you'll need something like a dual sync monitor (E.G. C= 1942) to display them. Multisync monitors like some of the MicroVitec ones are also very good.
If you get a scandoubler, which doubles the 15kHz scan rate to the 30kHz required by "PC" monitors, then you can use pretty much any off the shelf analogue SVGA type monitor, with a few exceptions..
As far as other accessories go, you can use any IDE hard drive, or SCSI device if you have a SCSI controller. Also centronics printers, serial modems, etc.
If you add a USB card to your A1200 it'll let you use some USB devices like removable media, PC mice, USB scanners, digital cameras, etc.
If you get one of the PCI soloutions like a G-Rex card, you can use some PCI video, sound and TV tuner cards.
So there's a lot of extra stuff you can do if you're prepared to expand things.
