Imported Driftwoods.
Spiderwood is buoyant and can float upon initial use.   
low tanin contained.
Branched wood. give your scape extra detailing. One of the popular collection in aquadcoaqua nature gallery
Prolonged boiling recommended,boiling/soaking for 3-4 hours. You have to boil it for at least an 1 hour (maybe twice boiled and dump the tannin concentrated water midway both times). Afterwards, completely submerge the wood in a bucket with water, weighing it down with something i.e. a rock , heavy glass cup etc, until it doesn't float anymore when the weight is taken off.
High quality woods thats why long lasting at underwater.