Easy Spoke Length Calculator (as long as your hub & rim are in the database)
http://www.prowheelbuilder.com/spoke/index.php
I've been tinkering with wheel building or a little less than a year. I just purchased a Park TM-1 spoke tension meter a couple days ago, and haven't yet had a chance to use it - so I can't yet say if it'll make much of a difference.
I'm a clydesdale (270lb), so my bikes certainly get their fair share of abuse, even though I typically ride less than 200 miles a month. I've only had one wheel fall apart on me (broken spoke, loose spokes)...and it wasn't a wheel that I built. It was a WTB Laserdisc that I bought new, and had less than 100 miles on it. I've since replaced the spoke, and re-built the wheel. I've put nearly a thousand miles on it since, and haven't had to even re-true it.
Everything I learned about wheel building & truing was on Sheldon Brown's website, and YouTube. So far, it's paid off.