Must Have Applications and Can't-live-without Websites: My List. What are yours?

I've used thousands of applications and websites over the years, and I thought it might be useful to share my favorites with you. I'm sure I'm missing some great ones, and would love to hear your favorites in the comments!

Part 1: Applications

Tweetie (Twitter client for Mac)
In my opinion, the best Twitter client for Mac that's currently available. Sleek design, easy navigation and control and wonderful support for multiple accounts. There's a free version, which throws in the occasional ad, or you can pay a few bucks for the pro version. I've played with all the Twitter applications fairly extensively - this one is the king! The only downside is that it doesn't support grouping of users like Seesmic Desktop or TweetDeck.
URL: http://www.atebits.com/tweetie-mac/

Skype (communication)
Skype is how the modern web user communicates. Whether your looking for regular chat, or VOIP/Video chat - this free application is a must have. It's also becoming ubiquitous so chances are the people you want to connect with have it also.
URL: http://skype.com

XMind (mind-mapping)
This free software is the best I've seen for creating mind-maps, fleshing out ideas or creating just about any kind of structures chart. I've tried the expensive programs, this one beats them easily. Hint: If you're going to use XMind, you'll want to learn the keyboard shortcuts.
URL: http://www.xmind.net

Evernote (Clipping notes, ideas, images, etc. from the Web)
Evernote (Mac, PC, iPhone, Blackberry) is an awesome tool I didn't realize I needed until I had it. I can easily clip anything to Evernote, add notes of my own and synch the notes to all of my devices. A software journalist could explain better why you might need this tool, but I think anyone who spends a good amount of time on the web just does.
URL: http://www.evernote.com

Seesmic Desktop (Twitter client)
My second favorite Twitter application is also my first when it comes to Groups. Sometimes I don't want to sort through my entire stream of Tweets - especially when I'm catching up after being away for a while. Seesmic allows me to create groups so I can focus on tweets from the users I choose to focus on. It's also good for managing multiple accounts and supports Facebook updates as well. If I could only have one Twitter application, it would be Seesmic because it's well rounded (until Tweetie comes out with group support).
URL: http://desktop.seesmic.com

Blogo (blog editing/posting for Mac)
Back when I used a PC as my primary computer, I relied on Windows Live Writer to post to my blogs. Instead of logging in and using the blog softwares editor, I could use a more sophisticated tool and then just upoad them when I was done. After moving to a Mac and realized there was no Live Writer for Mac, I was quickly pointed to Blogo, and it's been a great replacement.
URL: http://www.drinkbrainjuice.com

NetNewsWire (RSS Reader)
NNW is a powerful RSS reader. It behaves like a desktop mail client and includes all kinds of powerful ways to manage your feeds. If you use RSS and have a Mac, you probably already have this software. Unfortunately there's no Windows version and the equivelant is just not that good. NetNewsWire replaced Google Reader for my RSS reading needs.
URL: http://www.newsgator.com

Bit.ly Sidebar (URL Shorterner and then some)
If you use Twitter, chances are you've used a URL shortener and you know what they are, so I'll conserve space. The bit.ly sidebar adds a little extra flavor though, in that it's a bookmarklet that lives in your browser, and when activated it will provide you with a shortened URL for the page you are on, as well as show you other tweets which include that URL and some basic stats. Very cool.
URL: http://www.bit.ly

So? What did I miss?

Keep an eye out for Part 2: Websites and Part 3: iPhone Apps