35% VTI (Total Stock Market Index)
35% VXF (Extended Market Index)
15% VXUS (Total International Stock Index)
15% VSS (All-world Ex-US Small-Cap Index)
Vanguard recommends 70% total US and 30% total international, so I went with that for my US/International allocation. But I wanted to tilt towards small and mid cap companies for the potential of greater gains. I looked at several different allocations using Morningstar's Instant X-Ray and Personal Capital and this is the one I liked most. It's also very easy to maintain by having my US allocation split 50/50 between 2 funds and the same for my international allocation.