I'll assume no taxable investments except perhaps a MMfund with 12 months of expenses. The IRA will then hold:
25% VTI Vanguard total stock market
25% VEU Vanguard FTSE all-world
25% VIPSX Vanguard TIPS, but pick the admiral share class
25% VFIIX Vanguard GNMA fund, but pick the admiral share class
If you wanted more risk, then move up to half of the VTI (12.5% of portfolio total) to VBR Vanguard small cap value and/or move up to half ofthe the VEU to either GWX or DLS or the soon-to-be opened Vanguard small cap international ETF.
As market goes lower, I'd sell out of the GNMA fund and move to the equity ETFs until I had about 60% equities.
oh, full disclosure: I own shares of VTI, VEU, VIPSX, VFIIX, and GWX. Instead of VBR, I own IJS.