Hmmm. Here's a problem that I'm going to end up building a solution to if someone else doesn't do it first (and by all means, please do it because I am lazy and have enough projects to last me for the foreseeable future):
A CRUD application generator. You go to a page and define all of your models and basic rules. The models get defined in very simple terms - you give each model a name, and then define each field with dropdowns that define what each field is. If it's a foreign key, you select that in the dropdown. You can select validation for each field from a catalog of validations (phone number, email address, string min length of 5 chars, whatever).
Offer addins for commonly needed functionality - for example, I end up using authentication in just about every project and end up having to do a lot of work to get it up and running. So you could have plugins like authentication, private messaging (which would require auth automatically), a ticket system, whatever.
Also offer the ability to choose a theme before generating a project.
So a user can go to a site, define their models, add any addins they want and pick a theme.
Then in the final step, they choose a language and framework they want everything generated in: Python / Django, Ruby on Rails 2.3.x, Ruby on Rails 3.x, Python / Pylons, Scala / Lift, ASP.Net MVC; whatever templates you've gotten built.
When it's done, they get a compressed file (zip or tar.gz) that contains the generated application and some programatically created documentation that explains where everything is, how to change the important parts and how to deploy it.
There are lots of ways to make money with something like this:
* Charge for addins per project
* Charge for premium themes
* Charge a small amount per project (I like this option the least)
* Provide automatic hosting a la Heroku for projects - this would let people with a basic idea but no programming chops get something up in an hour or two instead of trying to find someone to explore the idea with them. For this you'd want to limit it to a subset of frameworks so that you don't have to have a lot of different production environments.
* Use a fremium model where people can generate x number of apps a month for free, but over that limitation charge some amount per month. People will try to get around this by registering with multiple email addresses if the product is good, but that's a great problem to have!
Although it sounds like you're probably somewhat freed from a profit motive while you're building this, which helps significantly. From a dev perspective it would be fun to learn enough about all the major frameworks to generate sites in them.