You can do multiple HDMI but you lose audio, since it will only provide audio through one output.
Also you cannot drive 3 HDMi via the DVI+HDMI+DVI of a card like the HD5870 etc because you only have 2 sets of TMDS and thus only one DVI will work if the other is powering the HDMI.
For single card you need either a dual GPU card that supports quad DVI out, and then doing the DVi-> HDMI conversion, or else getting the HD5870 Trillian 6 Display port output and then using active converters for HDMI.
Now the most cost effective way is to have 2 separate cards like the HD5450 if you're not gaming or else equivalents depending on power needed 5670 or more for more power. However do NOT crossfire them it complicates the monitor support, just hook them up to the 4 outputs/inputs.
But once again you are stuck with just a single audio output.