The following links are specifically for photographers.  If you are not a photographer, you'll find these remaining links both useless and boring.  I have used the products or services of these vendors and can recommend them.  I briefly describe each company's virtues.

Mamiya USA:  Great Optics and rock-solid construction make their products the choice of many professionals.   Mamiya USA also handles the highly-regarded Sekonic meters and Profoto lighting equipment. 

http://www.mamiya.com/

Nikon USA:  Like Mamiya, Nikon produces great optics and rock-solid professional cameras.  Nikon and Canon dominate the 35 mm film and digital SLR market and professional rental firms generally stock primarily Nikon and Canon in these categories.  Though I don't use Canon cameras, they are every bit as good as Nikon and appear to be retaining their dominant spot in the Digital SLR market. 

http://www.nikonusa.com/

Fuji:  Their digital SLR cameras are wonderful tools for the portrait and wedding market.  If you do portrait work and have no desire to shoot RAW and convert, you'll find no better camera for JPEG files straight from the camera.  This is particularly true of the new S3 with its extended dynamic range.  If you are a sports or commercial shooter, you might be better off with a different brand. 

Fuji film is great too.  Some labs and photographers prefer Kodak and others Fuji.  Let's just say that as long as they are both fighting for the same market and each is raising the ante, we will all benefit from the race.  

http://www.fujifilm.com/JSP/fuji/epartners/index.jsp

Photogenic Machine Corporation:  I've used their lighting equipment for about 9 years and, though it  may not be quite as sophisticated as the far more expensive European brands, it's solid and workman-like.   Their lighting accessories (reflectors, barn doors, and grids) are pricey, so keep this in mind when considering Photogenic.

http://www.photogenicpro.com/

Novatron:  Some commercial photographers may laugh at me for saying so, but if you shoot on-site portraits, and minimum weight and great bang-for-the-buck are important, Novatron Pack/Head systems are quite good.   Fine tuning the lighting is easy with a combination or their unique reducing heads and  new packs.   If you can live with the cheesy plastic housing on their regular heads (bare-bulb head is all metal) and the paucity of Novatron-sourced reflectors, you won't be disappointed.   Note: if you will be using softboxes, go with the bare-bulb head.

http://www.novatron.com/ns/index.php

Quantum:  The quantum Q-flash series of portable flash equipment is very versatile and solidly built,  but you pay a premium for the quality.  I love the bare-bulb configuration for events where a white ceiling is available.  Great for the working pro, but probably overkill for the weekender.

http://www.qtm.com/

B&H Photo Video:  I have always had good luck with B&H, and a large proportion of my photographic equipment and supplies have been purchased through them.  The world of photographic sales in NYC has not always been on the high road.  I credit B&H to a large extent with  leading the charge for ethical and customer-focused sales.   Should you visit their excellent showroom,  you'll become immediately aware that  B&H has intimate ties with the Brooklyn Orthodox Jewish community.  If you listen you'll hear the occasional exchange in Yiddish.  Enjoy the cultural difference and don't be put off by the matter-of-fact delivery that you may receive from some of the guys.  Behind that Jack Webb just-the-facts facade is most likely a wicked and wry sense of humor. 

http://www.bhphotovideo.com/

Unique Photo:  I have been happy with all of my purchases through Unique and their pricing is very competitive.  They are now getting an increasing amount of my purchases.

http://www.uniquephoto.com/

Calumet:  I've received excellent customer service from Calumet and they carry a number of items unavailable elsewhere.  They do not deal with gray-market products and I have always received the freshest supplies from them.   On the downside, they are bit more expensive than some of their competition.

http://www.calumetphoto.com/

Bogen:  Distributes first-rate products.  If Bogen represents it, you can be fairly certain the product is competitive with the best in its class.  Bogen imports such well-known brands as: Elinchrom, Gossen, Manfrotto, Lastolite, Gitzo, and Metz.   Bogen is not a retailer. 

http://www.bogenimaging.us/