So it looks like we've got:
TextEdit - free and pre-installed
Text Wrangler - free, not sure if on the App Store
Taco HTML - $25, available on the Mac App Store
TextMate - $55
Espresso - $80, www.macrabbit.com
Flux - £70, www.theescapers.com
I believe there's also one called HyperEdit that's only $15 on the App Store, but it hasn't been updated in about 2 years. I haven't tried it, but I hear it has a feature to automatically check your code for compliance (to HTML 4.01 or...