[petervandijck]

There are some developer-oriented startups that are doing well, like the one that sends emails for your service (can't remember the name, anyone), it's basically just an API. Dropbox as well is mostly backend and code and algorythms, very little UI. Stuff like that.

If you can do something that's hard and high-value for developers with their own startups, and expose an API, that might be a good startup. How about a face-identification/recognition startup?

Database startups (nosql stuff) are hard, but also being done (again, can't think of the exact name, anyone?). But then you're likely gonna be in the consulting business, apart from building a kick-ass database.

Another example: janrain's RPX, again, it's mostly just an API and code to mangle all the social services' api's, very little frontend, although there is definitely sales/consulting involved..

[albertmg]

I suppose you're talking about http://www.mailchimp.com/ for email service

As for database startup there are plenty of them too: cloudera.com, percona, schoonerinfotech.com , ...