I bought the Pixel Ruler from UI Stencils for US$29 (S$41) and shipping to Singapore is an additional US$14.60 (S$21) via USPS First-Class Package International Service.
The Pixel Ruler is a good tool to have for responsive screen size sketching. It is a heavy-duty gauge stainless steel ruler with pixel increments. There are markers on the ruler for mobile, tablet and widescreen (laptop) sizes.
