How do I monetize my Website (100K visitors a month) and iPhone App (20K downloads)

Re-visit your marketing strategy. Which is to say - re-visit your business model (which should very directly point you in the direction of your highest probability marketing strategy).

And (get ready to not like me for saying this...) stop focusing on those numbers. The number of visitors per month and the number of downloads are only relevant as they directly relate to conversions and sales.

And those things are only relevant as they directly relate to bottom line revenue and margins.

It's easy to get caught up in "vanity numbers"... those numbers that "feel good" and provide you with a sense of validation. But until and unless they translate into bottom line income for the business they are just numbers that make you feel good (versus wisely chosen key metrics that indicate the health and viability of your business).

If this was helpful to you please let me know how else I can be of assistance.

You need to create a marketing funnel that gives you several levels of conversions. I tend to name these Lead -> Prospect -> Activated Customer -> Repeat Customer. Organic traffic is all well and good, but is it targeted and segmented? You could have an information products business or an affiliate marketing business or one of several other business models. It all comes down to evaluating your site and seeing where the value is for some segment or segments of your audience in order to engage them in a buying relationship. Customer activation is without question the most important piece of a business like this. Happy to discuss with you if you'd like.