iPhoto'08 has a calendar feature that makes it very easy to create a wall calendar. It has a bunch of built-in styles and themes, but beyond those, it's not very flexible.

The standard page layout is landscape mode on US letter paper, one page for the picture and one for the month. The Print dialog lets you change these, but with unexpected results: when I changed the paper size to A4, the picture and month printed out in portrait mode (with large white spaces above and below).

After several hours of trial and error, I found a solution:

1. With the standard settings, click Preview in the Print dialog (or Export as PDF).
2. In the Previewer, click Print, then in the dialog, select A4 paper size and desired layout (eg two pages per sheet). If necessary, select Automatically Rotate Page and Scale Page. Then print.

[robg adds: I haven't tested this one.]