I'm looking for a travel guide (i.e. book) to Kaliningrad. Are there any particularly useful English-language references for visitors to Kaliningrad? I am particularly interested in any remnants of the old Königsberg.
Although I still consult the default guides (e.g. lonely planet, rough guide), I find my self more and more to rely on online resources, specifically build around satnav devices.
My three favorites are 1. Geocaching.com, 2. routeyou.com, and 3. Everytrail.com. Geocaching is nice, specifically if locals engage in this fun activity. Then again, you need to speak russian to appreciate the caches to the fullest.
So although these three online resources don't provide an extensive source on written descriptions, all provide interesting focal points in any destination, at least in my experience.
Routeyou has a very interesting route in Kaliningrad. In never realized that the in mathematical circles well known Travelling sailes man problem is actually based on Kaliningrad Source: Wikipedia.org
Königsberg was destroyed during WWII, and then reconstructed. So there are some old houses, but not as many as you can hope to find.
As Mark said, you should start with Cathedral, and Kant's Tomb.
You can find much more information in this answer.
There are also good online guide.
Well there are lots of sites online that cover this.
For example you could look at Wikitravel's page on Kaliningrad.
It looks like the top site from the old capital Königsberg is the cathedral, built in 1333. There is an English-language page on their official site.