Ask HN: What is needed to rapidly build mobile apps?

I am thinking of creating multiple mobile apps using HTML5 using rapid prototyping. In order to bring them to market fast I am trying to use as much outside services as possible but keep the costs as low as possible. My current list is as follows -

Backend - Parse

Visual Design - Outsource using 99 designs

Analyitcs - Flurry

Testing - Device anywhere

HTML5 application development using - Phonegap/Titanium/Sencha

What else would you add to the list? Am I missing something obvious?

PhoneGap and Titanium are mutually exclusive.

Sencha would work with PhoneGap, in that you need HTML/CSS/JS to put into PhoneGap.

Be careful with 99 Designs. You're more likely to get a design that will be almost impossible to implement on top of Sencha, unless you give a lot of feedback to the designers. Given the cost of getting a mobile app design there, you'll need to stay on top of the process to avoid wasting money.

Thanks for all the suggestions. I am adding few more things that I forgot earlier -

Stress Testing - ???

App Distribution - Zubhium

App Marketing - AdMob, AppSurfer, AppBrain

Also, is there some service that can provide initial validation of an idea. I need some service through which I can contact 20 users and ask them if they will use a particular app and if so how much will they pay for it and what features they would like?