I don't believe any can yet due to the insane reso. However, if you want a cheap(using that loosely) 1080p TV you can always get a 24" monitor. There are many HDCP 24" monitors.
1080P is considered "Full HD" as they claim.
You are correct. The problem is that 30" monitors require dual-link dvi, which isn't compatible with any hd source directly. You could do HD through something like eyetv hybrid, though, but you would be limited to unencrypted signals (something like the tvmini hd+ does do clear qam, but not all cable/sat providers give you much unencrypted hd). once leopard comes with blu-ray (and hd-dvd?) support, you should be able to get a blu-ray drive to display, but you would need an hdcp compatible video card, too. The fact that video devices aren't dual-link (hdmi is single-link dvi + audio) is, in fact, the reason that the 30" dells don't have multiple input sources (essentially, to get that high a resolution, the video card sends half the singal over each part of the dual link; i honestly don't know if it is physically half the panel, or every other line, etc., but nonetheless you can't display a single-link through it at full resolution).
cheers.