I love cross-platform open source.

I'm so in love with open source. And unix. And cygwin.
./configure
make
make install

Those three commands lead to such goodness. At the moment I'm installing FreeType2, a free, high-quality, portable font engine. I'm installing it on my windows tablet, but I'm entirely certain that I'll be able to compile and install it on the linux system at work with those same three commands... and that code I write on my PC will work under linux.

And, my favorite firefox feature: type anything into the firefox address bar. Hit return. You get the google "I'm-Feeling-Lucky" result. It's just... so... perfect.