Tweetie - Clicking this icon will bring up Tweetie and show me my latest tweets, DMs, notifications, and more from Twitter. I don’t really like the new Twitter for Mac compared to the old one, so that is why I still use the older version.
Adium - I love Adium and use it everyday. It is the best IM client on OS X by far. I have changed the menu bar icon to a 1up icon depicting a mushroom from the Super Mario games.
gfxCardStatus - My Macbook Pro 15” has both Intel HD and AMD Radeon 6750m GPUs in it, and OS X only gives the user to have automatic switching between both GPUs or using the discrete Radeon only. gfxCardStatus lets me use the integrated Intel GPU only so I can save on battery life when I am unplugged.
SMARTReporter - I always worry about my SSD and external hard drives’ health/S.M.A.R.T. status, so I keep this utility on at all times. I even have it so it sends me an email if it is starting to fail!
MenuMeters - From left to right, I have two aqua lights that show Disk Activity, then since I have a quad core Macbook Pro, it shows me the usage from all four cores. Memory usage is next, showing me the used and free totals, and lastly, we end with network, which upon clicking on it, shows me detailed information about my current network, which is through gigabit ethernet.
Airport - Currently off, as I use gigabit ethernet most of the time.
Bluetooth - Currently off, but I do have it on whenever I need to transfer a file or I am paired with another device.
Time Machine - I have recently reinstalled and haven’t plugged in my external Firewire drive as of yet. Otherwise, this icon is really handy to see how much OS X has backed up and its progress.
Sound - Usually I have an optical cable running from my laptop to my set of Logitech Z-5500 speakers and the icon would be greyed out, but I am currently away from my desk, so I am using the built-in speakers and the icon is usable.
Battery - I have my laptop battery on the left side and my APC UPS battery on the right side. I love to show both, so that way I know which one is being charged at the moment.
Time and Date - I have it set to 12H time and day only, because I am so used to clicking the icon and finding out the exact day.
Spotlight - I use it constantly. I just couldn’t use OS X without it.
(From Anchit Panchal)