The highest resolution that TripleHead currently supports is 3x1680x1050, or 5040x1050. This is a limitation of the bandwidth provided by dual-link DVI rather than a limitation of the TH2Go device itself, so getting a screen that is higher res than 1680x1050 is... not a waste of time, certainly, but... might not be to your liking if you dislike TFT panels running at non-native resolutions the way I and some others do.
Unless you're running old monitors that are VGA (D-Sub) only, don't get the analogue TH2Go - get the digital one.
Check out
this thread to find which monitors can and can't do 3x1680x1050 without issues - from what I understand the Dell 2209WA is well thought of. I seem to remember someone mentioning it was S-IPS as well, which is always a plus above TN Film type panels.