I've never seen a titanium valve before, only stainless steel or sodium-filled stainless steel.

Crower makes some nice slightly oversize stainless valves, part numbers 97408-I for the intake side and 97408-E for the exhaust, but they run about $300 for the whole set and are a special order item. Can't say I know how much of a performance gain they will provide though.

One thing to keep in mind though is that if you're building up the bottom end, going with a VTEC head will make you more power even if it's not built to the extent of the LS head.