I'm looking for recommendations of good software that are particularly useful for netbooks. Software that run great on small screens and low CPU/RAM requirments.

I'll start off with the following :

Operating Systems:

• Ubuntu Netbook Remix.
• Easy Peasy: A fork of Ubuntu Netbook Remix that was once called UBuntu EEE. It isn't just for eeePCs though. Definitely worth a look if vanilla Netbook Remix isn't cutting it. (MarkM)
• Damn Small Linux (Source)
• Windows 7: With trimming the installation or compressing the Windows directory to fit on an 8GB SSD. (Will Eddins)
• nLite: A utility to install a lightweight version of Windows XP without the unnecessary components (like Media Player, Internet Explorer, Outlook Express, MSN Explorer, Messenger...).

Utilites:

• TouchFreeze: To disable the touch pad while typing (Source)
• InSSIDer: Not only does it make it easier to find and keep a wireless connection, but it turns a netbook into the perfect mobile tool for troubleshooting wireless networks. (phenry)
• AltMove: Adds more functionality to your mouse for interacting with windows. (Rob)
• ASUS Font Resizer Utility and other tools by ASUS, specific to ASUS Eee PC series.

Internet:

• Run FileZilla FTP client for a small screen :

You can hide a lot of FileZilla's interface parts in the View menu, even the directory trees. Go into Settings => Interface and move the message log next to the transfer queue, if you haven't hidden them both or you want to see them. Select a theme with 16x16 icons. (Source)

IDEs and Text Editors:

• Best lightweight IDE/Text Editor: A question on Stack Overflow that has many good suggestions of IDEs and general text editors for programmers.
• What’s a good linux C/C++ IDE for a low-res screen?: IDEs for Linux-powered netbooks.

Online tools:

• Dropbox: Since the Netbook has limited disk space, you would like to use Cloud Apps like Dropbox and Ubuntu One so that you don't run out of space especially if you are on a holiday. Later when you go back to your desktop with big hard disk,you can take out the files from your dropbox repo. (Manish Sinha)
• Google products: like Docs, Calendar and Reader (aviraldg)

Web sites and software lists:

• Netbookfiles.com: Netbook specific software downloads.
• Software Apps to Maximise your Netbook Battery Power:

Netbooks are known for their portability. Not only are they small and lightweight but with their increased power efficiency, batteries can last much longer than conventional laptops. This also means you no longer have to carry a power adapter with you! Several brands emphasis the longevity of the battery as a strong selling point, and for those people who travel a lot, it sure is.

• Free Must-Have Netbook Apps:

Finding software for netbooks can present challenges due to limited hard drive space, processor power, RAM, and screen real-estate. That doesn't mean you have to do without essential programs. The apps below cover all the bases -- entertainment, productivity, security, and communication -- without compromising on performance or usability. Best of all, they're free!

• Useful Netbook Software:

With short battery lives and small resolution screens Netbooks, unlike many other computers on the market, could so with some specific software for their use.

Now, not all of those I’ve found are specifically designed for Netbooks, but all are relevant. And they’re designed for Windows XP.

The question is community wiki, so feel free to edit it.

Updated, thank you all for suggestions.