Browsrcamp comes up every so often as a tip or trick for testing web sites on Mac browsers when you don’t have a Mac. The free service gives you a jpeg screenshot of what a URL looks like in Safari. For testing a homepage or template this is fine, but it breaks down in a dynamic context (for example: a site where you need to log in or where you’re using DHTML behaviors or AJAX).
But there’s also a paid service that lets you VNC into a Mac and actually watch how your site behaves in any browser (and they’ve got some weird ones). If you had a short-term project that absolutely had to look right on the Mac, this would be a cost-effective alternative to actually buying one–conceivably $20 could get you through your entire testing phase.
Given the number of times I’ve almost run out to Fry’s and bought a Mac Mini in a panic, I’ll definitely be using this down the line.