A task-based SEO service for small businesses. Charge $29-79/mo for X tasks. Tasks are basically content creation or link building. If you template out HTML pages and build some niche sites, I think you could easily scale it to 25 or 50 customers ($1-2k/mo)

FYI my wife is considering doing this aimed at wedding professionals.

Here are some things that immediately come to my mind :

1) Design themes/templates and sell it on sites like themeforest

2) Write ebooks and share your knowledge/expertise

3) Write custom premium php scripts like HN, Reddit clone and sell it.

4) Develop premium wordpress plugins

I actually tried to go that route and turned back. There's just too much headache with WordPress to do it every day.

So what you ended up doing?

Still a CS student, WP was just a "funny or die" adventure for last summer. For now, I do client work and sharpen my axe with Haskell.

I wish I had an interesting idea for a web product.

Do people buy clone scripts?

I know at least a dozen people who want to buy a Reddit/HN clone written in PHP, integrated with Wordpress/Buddypress, mostly to use for niche community sites they have.

Setup a service converting PSD files into Bootstrap layouts. Huge demand and you could easily do 5~10 a month and make $1000 (depending on what you charge for each one).

Google Andre Chaperon spend 20 mins and read his stuff and you will be on your way...they key is finding the audience before you build