Lots of articles and blog posts about social media marketing list Tweetdeck, HootSuite, and TwitterCounter as "business-class" social media marketing applications and leave it at that.  If you're the local coffee shop, then that's probably all you need.  If you're a marketer held accountable for lead gen, conversions, etc. - then you're probably going to want a bit more...

Broadly speaking - social media marketing is all about listening to what's going on, engaging your audience, and measuring impact of your activity.  So here are some great apps - built for business - that can help further your social media marketing programs, all categorized into three buckets - listening, engaging, and measuring.

It is also worth mentioning that many of these apps do a little bit of everything - they just do some things better than others.  Depending on your business - you may want to test drive a service from one or all of the buckets...or maybe just focus on the apps in the "most important" bucket.

Listening

The need - You're probably big and people are probably talking about you on blogs, Twitter, etc. - whether you know it or not.  You might also be running lots of hard-to-measure campaigns, so "sentiment" and "buzz" are important proxies for impact.  Your need for coverage far exceeds what you can get from Google Alerts and Twitter mentions - you need to get the big picture from all of the Internets.  Reputation management is a core marketing activity.

The customers - Brands, CPG, Fortunte 500, PR firms

The players - Radian6, ScoutLabs, Visible Technologies,

Engaging

The need - You have lots of engaged followers, so you're managing lots of conversations.  Most of your social media marketing efforts happen through real-time feeds like Twitter and Facebook.  Size is less of an issue here - you might be small, but you still carry a big stick in the real-time conversation.  Or you might be on a team of people that are sharing engagement responsibilities for a single organization.

The customers - Brands, B2C, individuals, support organizations

The players - CoTweet, HootSuite, TweetDeck

Measuring

The need - You're all about numbers in spreadsheets.  You're accountable for a budget and the goals you've set related to business outcomes.  Buzz and engagement are important - but you're more focused on the bottom line.  Social media marketing is a lead/conversion generation channel - not just an engagement mechanism.

The customers - Retailers, B2B, conversion marketers

The players - Objective Marketer, bit.ly