Reputation Management Online

1.  Monitoring.
Maybe this is not the best place to start out but it could save you a lot.
There are a huge number of reputation management companies out there and there are a huge number that do little more than monitor your brand for you without offering any real solutions. They will use some of the great tools out there like Trackur, Radian, Buzzlogic, BrandsEye, Buzzmetrics etc. but they may only tell you that there is an issue.
If you want to know what is going on then there are much simpler and easier ways of building tools that will do pretty much the same thing, yes they take time to build and are an evolving project for most companies but they can save you a lot of money, if you don't want to build it yourself, have someone build the tool for you and then hand over ownership straight to you without having to incur a monthly fee (unless you want them to monitor and update it for you).
And yes, I can build you a monitoring tool, email me!
2.  Squash the Problem Before it damages you!
The PR time bomb is out there and it's so easy to manage it's unreal, your average 8 year old can set up a blog so why do so many corporate entities not do it? If you know there is potentially a problem on the horizon then tackle it straight on. That way your monitoring shouldn't go haywire!
3.  Authoritative Blogger Reviews.
Every market has it's bloggers, no matter how niche your industry there are authorities out there that could make or break your online rep. Reach out to the authors and get them to write about you (do make sure they include a link!) You can go down the route of paid blogging, personally I find it a little shady as it diminishes the value of that person's opinion. Hopefully if you get a leading blogger to write about you then they will generate comments on their site and hopefully stimulate other bloggers to also look at and potentially write about your brand.
4.  Domain Names.
OK, I'm teaching you to suck eggs but why are there still people not getting this?? If you are a prominent person or brand, chances are many people will skip search engines altogether and type in a domain name.  Make sure you own yourname.com or yourbrand.com. Google loves exact name domain names, so it’s not really hard to rank a .net, .org, or even a .info these days.
In the field of reputation management it's also looking at potentially damaging web names, www.yourbrandsucks.com maybe worth having if you thing people may want to attack you. Bear it in mind.
4.  Make Sure Your House Is In Order.
Making 100% sure your site is as finely tuned as you can get it and it's ranking as best as possible for it's own identity is important for so many reasons aside form reputation management, don't neglect the basics.
Basic On-Page SEO is pretty easy.  Most content management systems will create crawlable site architecture for search engines to follow and interpret.  If you are using outdated CMS that creates a lot of duplicate content or uncrawlable URL’s, the content relevance and authority is being severely diluted.  Canonical URLs are still an issue (the www. and non www. URLs), search engines still look at them as separate sites. 
I could go on and on but I don't really need to, if you are reading this and don't know where your on page issues are already then go back and have another look, or I'll let you know some great agencies who could sort that for you.
5.  PPC and your brand.
Some marketers will tell you not to bother spending on your brand name, well, I have to disagree. Firstly it's cheap, quality scoring will ensure you're going to get the best deal on your company or product names. It's a great insurance piece, if you slip in the rankings for whatever reason you can at least be assured that the paid search option will keep you in your customer's eye line. If you don't bid, someone else will, got a US competitor, well, it's legal for them to bid on your name!
6.  Subdomains/Subfolders
You really want to ensure your blog is taking advantage of the authority that your core site offers. There is a bit of argument over which is best, personally I have seen both work , search engines do look at subdomains as unique domains and can diminish the authority of the originating site but it's a bit of a judgement call.
As a general rule, don't duplicate the content you are putting on there and make sure you have somewhere for your blog, forum etc. to go that can actually be viewed and there is a valid separation of content.
7.  Copyright, TM and Legal issues online
Wow, it's a bit of a minefield, there are companies out there that specialise on online media so do speak with them but as a general rule if you are not defending yourself then the relatively low barriers to entry mean in creating negative brand equity can and will make you a target. Just as an initial guide you can always look at going to google with a DMCA request if it's clear infringement for domain name issues then look up the ICANN Domain Dispute Resolution Policy