Larry Swedroe bases his writing on academic papers and long time frames of stock data, so I'd suggest:
"The Only Guide You'll Ever Need for the Right Financial Plan"
http://www.amazon.com/Only-Guide-Youll-Right-Financial/dp/1576603660(Note you can buy a used copy for $7 with s&h, or many libraries have a copy)
I like other books of his better, but that one is more complete for what you're asking. It ultimately becomes your decision on two points:
1. appropriate bond percentage: You need to know when you'll retire. You can pick a retirement percentage as a target (25-50%?), and then move towards that percentage the closer you get to retirement. You're probably looking at 1-3% more bonds each year, depending on your retirement date.
2. US vs international: Anywhere in 20-40% is conventional. You would pick 20% if you're not that comfortable with international, but want the diversification benefit. There's always a chance diversification won't help you, so the more comfortable you are with that the closer you might go to 40%.