Prototyping on paper. POP in the app store. Take pictures, or import pictures from your photostream, and add hotspots with custom transitions.

I swear by http://www.invisionapp.com/

Hey everyone, First a big disclaimer up front - I am designer, co-founder of Fluid UI the mobile app prototyping tool. This is not intended to come across as advertising but given your specific question I would love to let you know about it.

http://www.fluidui.com/editor

We are working hard to keep things intuitive and minimal with a simple workflow for uploading and linking images. It also exports a flow diagram that illustrates the relationship between the screens. We would love to hear what you think of it both good and bad.

Thanks and really looking forward to the discussion here.

Cheers, Ian

Live view, just hover the area over your photoshop canvas and hide the app, and you can preview as you design. Not really a prototyping tool, but great for designing. http://www.zambetti.com/projects/liveview/

I like http://fieldtestapp.com and I wrote a post about how to use it.

http://blog.thoughtbrain.com/2012/08/24/field-test-prototyping-app/

There are alot of really good ones out there, but that one seemed to not overcomplicate things. I still need to do more in-depth review of some of the newer ones and older ones that have newer features.

AppCooker is pretty decent once you figure it out.

I like POP but it currently doesn't support the iPhone 5 screen, which I think is a pain in the ass.

http://www.appgyver.com/prototyper is $9 or $39 per month, but very robust and seems to be easy to use.

Awesome, thanks for the all the responses guys.

One service that I discovered during my search which wasn't mentioned here was http://proto.io, which I haven't tried but is maybe something one of you folks might want to test out.

keynote all day, literally feels like a real app if you're talking about mobile

It's still in beta, but you should check out https://www.flinto.com/. It's incredible -- the animations are so good that it looks like a native app.

Illustrator/Photoshop and Prototypes for Mac. Or Keynote. Or animated GIFs.

I like AppCooker if I'm fiddling about on my iPad. On the desktop, I'll make screenshots in PS and put them into Prototypes app, which can then install them on a phone via a code on the web.