One item I find really useful is a small screwdriver that fits into hollow axles (currently using a Torx T-15 or something). I clamp it firmly in the bench vise. After getting a couple spokes into the rim, I can just plunk the hub onto the screwdriver and then I've got both hands free.

After trying various spoke wrenches, I still default to the standard Park Tool loop models without the enhanced-grip jaw, because they don't have to be lifted off the nipple. But after lacing the spokes and running them up to the last visible thread with a BR nipple driver, I usually use a Wiha blade screwdriver on the nipple slots for the bulk of the build, then bust out the spoke wrench for finishing. Saves stress on my hands, for one thing

For starting slotted nipples in a double-walled rim, my Quick-Wedge 1836 screwdriver gets a lot of action: