The Amiga really has untouchable apps, Twistin'... Directory Opus is brill, so is DPaint. And I cannot do some music stuff with some PC programs. Musicline Editor is an awesome tracker/synthesizer.
Of course, the whole AmigaOS is brilliant. The best multitasking OS I have ever used.
About paint programs... if you don't mind only being able to work with 8bit resolutions, you can get Deluxe Paint IIe. It's got many of the Amiga version's features minus animation. However most paint programs should have a 'pattern' mode which lets you do just that. No warping though.