Professional window cleaning poles are curved towards the end for a better result when cleaning high windows, but they don't exactly come cheap. Specialist site Window Cleaning Forum details how to make one for yourself using a cheap pool cleaning pole and a few hardware store items.
The total price (in Australian dollars, no less) for the whole construction is around $20, though you'll need a heat gun to bend the irrigation pipe segment used to create the curve. You could potentially pick up a pre-curved pipe segment in the plumbing section, though matching the sizes to your existing pole might be trickier. It seems like a pretty straightforward process, but the post offers a detailed step-by-step guide.
For windows you can reach, newspaper remains a great cheap cleaning agent. Got your own self-constructed cleaning tool tips? Pass 'em on in the comments.
DIY Curve Pole for $20 [Window Cleaning Forum]