By 'valuable' we're not talking about hand regging $x,xxx names, except with the very occasional lottery-ticket convergence of events of course.
But there are still countless domains out there to hand reg that can bring you xxx, or if you're really good at selling, x,xxx.
The trick is to have a plan, a good clear plan, and to put in the smart work on it. You don't just hand reg names and let them sit there hoping for someone to send you an offer, you hand reg names with a plan in mind. Some examples of what are still working for people these days:
Niche/personal local names - there are a good number of domainers going this route, where you'll find a domain with search numbers for some locality, like LasVegasDuiLawyers dot com, or MiamiPaddleboardYoga or EastVancouverSkateboards, that kind of thing. More often than not it's a small city, or a busy burg of a large city, plus some generic business or service. Then you'll set a reasonable price a small biz could afford, usually in the $300 - 600 range, and work up an email list for end users. The domainers succeeding at this research each name carefully to make sure there seem to be a healthy number of possible end users for the name, in that specific locality.
Another: forward-thinking names. This is when you keep an eye out for any news items about ANYTHING new that might 'take off'. There is a constant bow wave of new tech and trends and products coming our way at each moment, you can literally find hundreds of new tech terms and word mixes, new catchphrases and expressions, new generic product terms, every single day. The canny domainers look into each one and try make an educated guess on which name might be worth regging, paying renewal fees for a year or 5 years, on the educated gamble that their term might explode in popularity some day.
Of course, this is a lot more gambling rather than solid plan, but if you keep your finger on the pulse of what seems to be hot and not hot in new trends, you might have a chance of a domain worth x,xxx or higher in the future. However, it is still a vague gamble and this kind of gambling is making registrars rich and domainers poorer, for the most part
I do this kind of regging very carefully... of the many new terms popping up, I average one of these gamble names max every month or two. Recently I've gotten like Grape Skin Powder (all these in dawt com), Rocking Skateboard, Tablet Phone Store (tablet phones look to be huge in the near future... I hope), that kind of thing. This kind of regging is more educated gamble than 'plan', but it's kind of like playing the lottery so a small part of your new-regs budget might be applied here.
Another: some domainers try to corner a niche market on names, regging a few dozen names with 'cloud' in them, or 'nfc' or some other keyword or new term. Kind of the 'if you reg 40 of them one is bound to sell for a great price and pay for all of them plus profit' thinking. To me this is kind of a real gamble too, unless you compile a very condensed list of names that you have researched and feel there's a strong end user base for each name. Not a vague end user base for the keyword, a specific end user list for each different name using that keyword.
Another: during the climb and peak of long-tail domain names, specifically for their minisite possibilities during the brief minisite heyday, tons and tons of natural search terms were regged by domainers, both newbie and veteran. With the plummet of minisites and adsense and parking income, these names are dropping like flies lately. To most, they're not worth the renewal fees anymore since they simply don't pay for themselves.
They become expired/dropped names, and there's a huge trade in them these days. You can reg expired/deleted names or pay a dropcatcher to try snab it for you. It's hit or miss: aim to catch names that you feel a strong plan for, something you research and find a good pool of end users to approach about. The good thing about this selection of dropping names is simply personal interest - a name you are attracted to and feel you can approach end users about, might not interest the next domainer, who is searching for different kinds of names. There are many domains dropping daily that domainers had no 'plan' for other than parking them, and since these names don't make enough parking income to bother with renewing, they drop... and become available to domainers who might actually have a strong sell plan for that name.
There are many more tactics being used, but there's a small selection of them for starters.
Good luck
