A new application called Digsby wants to tie together your e-mail, instant messaging and social networking accounts into a simple interface.

There’s an obvious need for something like this. When I’m working, I constantly try to juggle e-mail and IM — sometimes multiple accounts of both — and I know it’s a frequent complaint from others, too. Checking my Facebook newsfeed is probably a little less urgent, but it’s definitely something I do once or twice a day (cough, cough), so streamlining that process is a big plus.

The problem for Digsby, of course, is that it’s such a great idea that plenty of other companies have gotten here first. Last year, for example, we covered Fuser and Orgoo, two e-mail applications that tried to centralize communication by combining your mail with, respectively, your social networks and your instant messaging. In January, we wrote about Imo.im, Social.im and 8hands, applications that merge social networks and IM.

Yahoo also recently announced oneConnect, which aims to combine e-mail , IM, text messaging and social messaging on a mobile phone.

So there are plenty of companies approaching the all-in-one messaging application from different angles. But Steve Shapiro, the Rochester Institute of Technology MBA student who dreamed up Digsby, says his application is the most usable. After trying Digsby out for myself, Shapiro’s claim seems to hold up. Digsby is very, very easy to use, allowing you to follow notifications from multiple accounts through an IM-style interface. (See accompanying screenshot.) When it comes to keeping a program running in the background, an unobtrusive IM window makes more sense than, say, Fuser’s Web page and Orgoo’s e-mail -style interface.

Although Fuser told us it’s going to add IM, and Orgoo says it’s going add social networks, neither seems to have done so yet. It may not be alone for long, but Digsby appears to be the first to bring the trifecta of e-mail , IM and social networking together. (Right before we published the story, Orgoo co-founder Sean Rad contacted VentureBeat to say the company will be making an announcement Monday, so expect some new features.)

Shapiro says there are several other features that make Digsby stand out, including the ability to reply within an IM pop-up reminder, to send e-mail s from the IM window and to easily cycle through prior messages to navigate topic changes in an IM conversation.

One caveat: Silicon Valley was all excited about a similar development — unified messaging — about a decade ago. Back then, a bunch of unified messaging startups raved about the ability to merge voice, e-mail , fax and SMS. It was supposed to be a sure thing — how could the enterprise not buy into it? — but somehow it never really took off. So it remains to be seen if this new generation of all-in-one messaging will fare any better, although I, for one, think it has a good chance.

Digsby, now in testing mode, has been in development for two years, and there’s a team working on it full-time, Shapiro says. They’re privately funded, and Shapiro won’t give me any numbers.

I do have a few gripes about the product: Integration with chat rooms like Campfire would be great, and the fact that the beta only works on PCs can make a Mac-lover like myself pretty grumpy. Still, I was impressed enough that when the Mac version (which, along with a Linux version, is promised) comes out, I’ll install it right away.