1. .in - Like .cn but the English-speaking world will be able to appreciate the upside of this extension whereas with .cn there are uncertainties (will there be IDN exts, is it better to go pinyin or IDN, etc.). We haven't seen many 5-figure public sales, but I don't think a lot of the bigger .in sales have been public.
2. .us - Has grown a lot and will continue to, some people still not realizing the power in this ext.
3. .tv - "Premiuming" the top .tvs is REALLY hurting this extension, but with online videos all the rage, I think .tv will see some more popular sites in the near future. It and .us are the easiest ccTLDs for Americans to remember.
4. .org - It's only #4 because people have started to realize that some amazing .orgs just sit there with all the other top 6 taken. .info best sales still haven't reached .org's best sales, and yet most people seem to think .info is better.
5. .net - .net is more or less on a low right now and will get back up sooner or later. LLL.net has become a really active market, maybe even more than LLL.com, simply because they're more affordable but still high enough to be considered fairly desirable.
6. .cn - It DOES represent the most populous nation on Earth. Language barrier hurts a lot though.
7. .co.uk - Well, underrated by everyone outside the UK. This extension does see some amazing sales here and there.
8. .co.in - I DO think that .co.in will ultimately be 2nd to .in, but even still, people forget about it and it's still the more established ext within India.
9. .es - Spaniards seem to be avid about it plus it's very domain hack-friendly
10. .sc - Call me crazy, but somewhere out there are more people intending to brand .sc = Source. I've got some good ones, so I might be doing it soon enough. It's also pretty, not as pretty as .cc, but .cc has been failing to really capture the spark for a long time so it holds no place on this list (someone earlier said "I think one day, .cc will take off" and I said that 3 years ago, still waiting). Most people value .sc along the same lines as .ms, .gs, and other lower-end ccTLDs, and I respectfully think they're wrong!