.co.uk
.net
.de (under valued for english keywords, worth investment)
.org
.info (under valued, worth investing in)
.us
.ca
.biz (most businesses don't care if they don't have their .biz as long as they have their .com or .net!)
.cc (don't waste money on this, it's useless)
.eu (although this works well on airlines, banks and other international businesses that operate within Europe such as currency exchange businesses)
Damn, ditto on this.
As for one and two, if you are in the UK and know the European market, go with co.uk. Strong market for generics and keywords.
Net is acceptable for many european countries so still a good choice. Also widely popular with Asian market. I have a few getting several thousand hits a month but the PPC is pitiful for the Asian searches. For the European and American seaches, respectable PPC.
.de is hot right now. Germans are very proud and loyal natives to land, product, and heritage. Curious to see how the English words hold up.
.org is universally recognized for what it is perceived...organizations. Registering words for this for the sake of registering can sometimes be worthless just because it is available. There have been some spectacular sales in this arena lately. If you find the list, you will see why. The domain name should be very applicable to the extension. That is the key with this as well as several others.
.info is massively under-appreciated and under-valued with prime keywords and generics available for pennies on the dollar in the secondary market. But it is catching steam and making some serious moves.
.us has restrictions, no one follows them, may not ever catch on fire but also good for domain hacks and finding some great keyword drops and generics. Some of my generics are doing exceptionally well parked with good conversion and PPC. There was an upward trend recently that may have leveled off with the focus on other extensions and news. But still worthwhile if prime and reasonably priced.
.biz may never catch on. But that does not mean there is good secondary market catches or drops. Only prime letters and keywords and strong generics. Some can be had for less than $10 bucks on the drop and are worth holding onto. I do have one LLL.biz that is getting fabulous traffic and decent PPC as it corresponds to a Russian Stock Exchange market.
.cc and .eu...eh. .eu was and is rift with so much corruption and poor management from the get go. I do not think there is a chance of this trying to pull through thanks to strong ccTLD's like co.uk, .de, and .fr, .es, .it, and .nu looking good. If there is one domain out there not necessary and will never find a home it is the .eu. There will be a similar one soon to be released.