Are you after advice on graphics cards or monitors?
If graphics cards, a Gigabyte Quad-Royal motherboard will be able to handle 4 PCI-E graphics cards. Search Anandtech to find out how to run 10 (!) screens.
Card-wise, almost all PCI-E cards have dual DVI outputs, link a pair for 4 outputs.
If more are required, perhaps a Matrox TripleHead adapter? Although it may not work so well for horizontal monitor setup.