For speedlights, you have to decide if you wanna drive stick or automatic—AKA manual or TTL. I live in manual mode, which means I sacrifice some convenience for reliability and repeatability. It also means I can pay about a third as much for each of my flashes.
If you live by TTL, you will die by TTL. Or, at least your wallet will die a small, unnecessary death every time you need to purchase a flash.
For manual speedlights, I wholeheartedly recommend the LumoPro LP180, about which I go into far more detail here. It's built like a tank, syncs four different ways, has a fluid and intuitive user interface, a built-in light-stand socket, a built-in gel holder and has a two-year manufacturer's warranty. No other speedlight comes close to claiming all of those useful features.
That it costs about a third as much as you would pay for an OEM branded flagship TTL flash is icing on the cake. If you can commit to shooting manually, this is your flash.
If you need TTL flash control, my current recommendation is that you probably stick with the branded flashes from your camera's manufacturer. Yes, they will be much more expensive. But adding TTL also adds layers of tech with related compatibility issues. So you probably want to cough up the money and stick with your camera's brand.
But at least consider you may be paying a tax on your lack of confidence. I can't remember the last time I used TTL flash. If you really feel you need it (for run-and-gun stuff, for instance) here's an idea. Maybe get one flagship branded flash. And then flesh out your lighting bag with LP 180's.
Don't Do This:
On the opposite end of the spectrum, there are a ton of flashes constantly hitting the market from the far east, from a variety of pop-up brands. Some of the brands are even zombies risen from the dead of brands that you used to know. They have spotty track records for quality. Factory warranties are short to nonexistent.
Many who read this will be tempted to go that route because of prices that are almost too good to be true. If that's you, by all means knock yourself out. Some people need to be stung in the wallet to remember a lesson or bit of advice. I know I did when I was young. Good luck with that!
As far as big (i.e., "studio") lights go, there is a completely different set of variables to consider. Big lights are system-oriented, and you would do well to choose wisely in what will likely be a long-term relationship.
I am happy where I am now. But boy did I waste a lot of time and money to get here.
You can spend a ton of money on Big Lights. The marquis names (Profoto, Broncolor) are silly expensive, and really only make sense if you are regularly shooting big-ticket jobs.
You don't need to mortgage your house to have good, powerful lights. And I think the sweet spot is in three brands.
Paul C. Buff
A good value choice for US folks, but not in other countries as PCB is mostly a domestic US brand. Skip the cheaper AlienBees models and go for an Einstein 640. It's a lot of flash for the money—much more so than the similarly shaped AB's.
Paul Buff also has good battery options which make the E640s great for outside, and a wide range of reasonably priced modifiers.
PCB brings a lot of advantages, but global availability (and cross-platform compatibility) is not a strong suit.
A good choice anywhere in the world, Elinchrom has made great strides lately in many areas. They offer powerful pack-and-head
kits that can be as much as six times as powerful as the Einsteins mentioned above.
They also offer a range of other models, including monoblocs and an especially cool ELB 400 (seen above) that is a diminutive, go-anywhere 400 watt-second flash that runs on equally small batteries.
These are full-system flashes serving a global platform. So you are not restricted by location, as you are with PCB lights. And Elinchrom offers a huge range of light modifiers that will allow you to shape your lighting in any way you want.
Even more exciting is the cross-licensing that is happening—especially with respect to remotes—that is happening with Phottix, below.
Not a "Big Light" company per se, Phottix' portable entry to the Big Lights arena is the Indra. If you are looking for a lithium battery-powered portable light that will allow you to work against full sun, this is a strong consideration.
Good value, strong build quality (important in a traveling light) and increasing cross-platform compatibility with Elinchrom, above, will protect your investment going forward.
Don't Do This:
Again, I would implore you to resist the siren song of the super-cheap mystery brands from the far east. Among the littany of reasons: No long-term reputation, bad (if existent) warranty, bad service—and some downright electrical dangers.
But if you young and broke and need some hard-won personal experience of your own to dissuade you in the future, by all means go right ahead. (I'm being sarcastic here. Resist the urge.)