When done right, wheel building is immensely satisfying and it's obviously made much easier by having the right tools. A wheel jig is essential, as is a spoke key, but this little gem is a luxury guaranteed to speed up the process.
Using a nipple spanner is the quickest way of locating the nipple on the spoke and getting the first few turns done to hold it together. As with all DT products, quality is first rate - will probably be the first and last nipple spanner you buy.
Buy DT Swiss Tools from Chain Reaction Cycles, the World's Largest Online Bike Store.