Rather than replace Quicktime with VLC, you're much better off, in my opinion, installing the Perian plugin. It runs almost everything: <a href="http://www.perian.org" rel="nofollow">http://www.perian.org</a><p>I suppose I've also technically "replaced" my dock and Spotlight search with Launchbar, which gives you, essentially, an Apple-fied version of a command line. Hitting a shortcut (cmd-space for me) opens the app, and it auto-completes application names and common OS tasks for you. Quicksilver is an FOSS alternative that does much of the same.<p>Launchbar: <a href="http://www.obdev.at/products/launchbar/" rel="nofollow">http://www.obdev.at/products/launchbar/</a><p>Quicksilver: <a href="https://github.com/tiennou/blacktree-alchemy" rel="nofollow">https://github.com/tiennou/blacktree-alchemy</a><p>Finally, not a replacement, but anyone who runs Boot Camp or anything similar owes it to themselves to install NTFS-3G, to read and write to NTFS partitions: <a href="http://macntfs-3g.blogspot.com/" rel="nofollow">http://macntfs-3g.blogspot.com/</a><p>edit: Fixed a bit of formatting. Also, saw a few of these were already mentioned (at least in passing) while I was putting my reply together. Sorry about the repeats.