But I'm not gonna tell you which one to get. The best advice is to read around on some of the following sites, which gives a lot of useful information about a lot of automatic robot vacuum cleaners, and make up your own opinion.
I've made a collection of my favorite sites with a lot of vacuum robot reviews which come in handy when taking the final step to buy one of these precious helpers.
How to vacuum cleaners operate (good way to make up an opinion about how smart they are):
First you should take a look at this site. It's in german, but their illustrations tell you the most. On this page they have tested a lot of different robot vacuum cleaners with reviews, and have videos showing each robots path in the same environment with obstacles. Take a look.
24 robots: http://www.heise.de/ct/artikel/Saubermaenner-24-Saugroboter-von-200-bis-1150-Euro-im-Test-1321903.html
The Vorwerk Kobold vr100: http://www.heise.de/ct/artikel/Saugroboter-Vorwerk-Kobold-VR100-1394515.html
Just click around on the site and you will find a lot more information.
Forum with a lot of information:
On this forum you will find a lot of information from experiences useres, as well as you can ask questions and get feedback. Click around and you will learn a lot.
Webpage with reviews dedicated to vacuum robot reviews:
This page is dedicated for you.. Doesn't need any more of a presentation.
Some youtube videos:
Neato vs irobot roomba speed test:
Neato vs Roomba suction/dirt collection ability:
Vorwerk VR100 (remember this vacuum cleaner has improved a lot with newers firmwares):