Twitter directories such as Twellow and the newer WeFollow from Digg founder Kevin Rose can go a long way toward helping you find Twitterers of interest. But when it comes down to compiling a really focused list, you have to get your hands dirty and plunge around through a bunch of individual Twitter accounts, too.
Enterprise IT pros, I've done the dirty work for you here and compiled if not the ultimate list of enterprise IT and network companies, at least a pretty good one of about 100 companies. (For those of you I accidentally missed, please make your presence known via the comments box or email me at firstname.lastname@example.org. You can follow me on Twitter here. Keep in mind, though, that I have tried to limit this list to companies providing IT/network products and services to enteprise IT customers, not to service providers or OEMs. Maybe that's a list for another time.)
Warning: The writers of these Twitter accounts aren't going to make you forget about John Updike any time soon. Many spit out exclamation points like baseball players spit out sunflower seeds. Disclaimers are common, press release headlines are the norm and many Twitter accounts look as if they're placeholders, while the companies figure out what to do with the dang things. Some companies are represented by a PR/marketing person rather than a more formal, logo-ed account. But all in all the Tweeter feeds can keep you up to date on announcements and what other customers or partners are thinking. And of course some companies, like Comcast and Dell, have been roundly lauded for their use of Twitter as a customer service tool.
Some companies, such as Cisco, have multiple "official" Twitter accounts, from generic corporate ones to more personalized ones updated by executives, such as CTO Padmasree Warrior and Doug Gourlay, VP of Cisco's Data Center Solutions Group.
There's also DigitalCribs, which looks at consumer uses of Cisco gear. (And of course Network World's own Cisco Subnet). It looks like some guy named Francisco grabbed the plain old Cisco Twitter URL.
I've roughly organized companies by category below (and where needed have included a brief description of the company and/or tossed in a sample Tweet for fun):
DATA CENTER/NETWORKING/WIRELESS/STORAGE/UNIFIED COMMUNICATIONS
AMD: The processor company calls its Twitter feed: AMDUnprocessed
BlueArc: Network storage
Bluesocket: Enterprise mobility
Brocade: (well, their PR guy)
Cisco Systems: main news site (Also: CiscoDC Data Center solutions; Cisco IT Inside look at Cisco IT's case studies, best practices, and experiences; CiscoLive: June/July event in San Fran, 2009 that in addition to tech will feature the B-52s and other "totally rad" acts and Ciscotelepresence