For proper 1080p support, I believe you need to be looking at 24 inch LCDs.
Actually you get 1080p monitors in sizes as low as 21.5 inch, I am using 3x22" myself.
As for your adaptor worries sonicmixer, please read this.. http://www.widescreengamingforum.com/wiki/ATI_Eyefinity_-_Ecosystem_September_2010
Or there is these...
21.5" 1080p with displayport input:-
Dell 2210H - Screen Type = TN.
Dell U2211H - Screen Type = IPS.
HP ZR22w - Screen Type = S-IPS.
To name just a few.
You will find the
WSGF Monitor List quite handy ;)