Like Dia for Windows. Dia is a free structured drawing program that looks and acts a lot like Visio, but it's smaller, simpler, and snappier.
For a free alternative, Dia is surprisingly complete. There are few things you won't be able to draw with Dia thanks to its three dozen sets of drawing elementals, ranging from basic geometric shapes to electrical, circuits, logic, jigsaw, network, and flowchart symbols, just to name a few.
You'll also be able to insert photos, clone, group, and layer objects, and fine-tune alignment. The only thing I haven't found a way to do -- I suspect it isn't supported -- is to rotate objects once they're placed on the page.
Dia isn't the only alternative to Visio out there (I've also told you about Project Draw, an online app, for example) but Dia is small, smart, and free -- definitely worthy of your attention.