Maybe the first thing you need to think about is what to call your website. Unfortunately most of the obvious names are gone. Every 3 letter combination has probably been registered already, along with most of the 1, 2, 3 4,5 and 6 letter words in the dictionary and some of them which aren't, so you're either going to have to register your own name if it's still available (e.g. bobatkins.com - which isn't available of course!) or you're going to have to make something up.
Using your name isn't a bad idea if it's fairly easy to spell. If your name is Zbigniew Brzezinski, you probably don't want to attempt to register the domain zbigniewbrzezinski.com, but if it's John Shaw, johnshaw.com is pretty good.
Making something up means combining two or more short words into a name. Keeping it fairly short is good. While you could attempt to register the domain name "theverybestphotowebsiteontheplanet.com", it probably wouldn't be a great idea. Nobody would want to type that many characters and the chances of making a typo are high. Even with a simple compound name you have to be careful.
Let's take the example of combining "photo" and "pics". This makes "photopics" - or does it? From the way it sounds, it could easily also be "photopix" or "photopicks" or even "fotopics", "fotopix" or "fotopicks". Now remember what I said about obvious names being taken already? Well here's the situation for these names.
So as you can see, even domain names which aren't so good are already gone! All you're left with is a very non-obvious spelling option. Of course you can hyphenate the name, but do you think people will know whether or not to use a hyphen, and if they don't know, they probably won't. So you could look at the domain names foto-pix.com, photo-pix.com, foto-pics.com, photo-pics.com, foto-picks.com and photo-picks.com to see if they are available, but you have to ask yourself if you'd really want any of them given that the non hyphenated versions have all been registered.
Throwing two unrelated words together is a possibility, such as purplefrog.com, happygoat.com or yellowdonkey.com - but all those domain names have also been taken! Strings like "Mountain Light" would be great, but of course mountainlight.com has already been taken, as has "PixelMagic" and most similar names. You could be lucky and be the first person to think of a really great domain name, but the odds are against it.
You can make up words for names like yozzy.com, pixota.com or truba.com - but you'll find all of those taken as well. Most short character strings that even sound like words have been registered. Not all of them, but most of them.
One way to look for names is to first pick a main word related to photography. That could be Camera, Lens, Image, Pixel, Focus, Aperture, Iris, Photo, Picture etc. Then you can create a list of prefixes and suffixes which you could add to those words. Some examples might be Best, Light, Sharp, Clear, Shop, Better, Unique, Work, Play etc. If you look at all the combinations of the two sets of words, something may emerge which sounds reasonable and hasn't been registered yet (though don't bet on it!). I have the domain name "LensPlay.com" for example. "CameraWork", "CameraPlay" and "LensWork" were all taken, but at the time (2001), LensPlay wasn't. Of course 7 years later, it's a lot harder to find unregistered name combinations.
So be prepared for a long quest for a good domain name. The main reason to do it NOW is that the sooner you do it the less likely it is that someone else will have had the same idea and registered the name before you get a chance to. As of early 2008 there were 160 million domain names registered and in the first 3 months of 2008, about 14 million more were added, so you can see that the competition for names is pretty fierce. Not all domains are used, in fact maybe 1/2 of all registered names are not associated with a website. They have been bough on speculation, hoping that they can be resold for a profit. A domain name can sell for anything from under $100 to over $1,000,000 depending on how good it is and how much someone wants it. The name "Business.com" reportedly sold for 7.5 million dollars and "Porn.com" is said to have changed hands for 9.5 million dollars. If there's a billionaire out there called "Bob Atkins", feel free to contact me about "bobatkins.com"!
Do you need a .com? Well, it doesn't hurt. It's the default extension and it's the one that everyone on the web knows. If someone tells you to "checkout the Google website", you'll type in google.com, not google.net or google.org. Some browsers will look for websites if you don't provide an extension - but they look for .com first.
Now .net or .org are OK sometimes. Photo.net does very well , but it's an old and well established site. My advice would be to try to find a .com name, but if you have a really good name and only .net is available, it might be OK. Just take a look at what the .com version leads you to. If it's a site that would directly compete with you, taking the .net version might not be a good idea as you'd probably be sending them some of your traffic.
There are domain name generators and domain name finders all over the web. Many of them allow you to type in keywords and the site will generate all possible combinations of them, then check which ones are available. One such site is snapitnow.com, though there many others.
You can also check out lists of recently deleted (expired) domains at sites like DeletedDomains.com. However you'll probably find that most of those names are pretty awful, which is why they were allowed to expire. A good domain name is worth a lot of money and some have changed hands for six-figure sums. If you had cars.com or photography.com or insurance.com, you would not let it expire!