Use a URL to link to a Google map with a marker on it

I want to link to google maps at a particular location with a marker on a particular point.

It's easy to link to a location:

http://maps.google.com/?ll=XX.XXXX,XX.XXXX

But how do I drop a marker at that point too? preferably with a bit of my own text but that's just a bonus.

2017 - Google has released documentation on this see new accepted answer: https://stackoverflow.com/a/44477650/359135