AntiVir
http://www.free-av.com/
A free (as in beer) anti virus scanner. Works on Windows, Linux, BSD, Solaris. Does not contain any big bloated interface with skins. Does not eat up all your processor power or memory. Simple and great.
7-Zip
http://www.7-zip.org/
File archiver that supports alot of format such as 7z, ZIP, CAB, RAR, ARJ, GZIP, BZIP2, Z, TAR, CPIO, RPM and DEB. It is completly free software which is released under the GNU LGPL, its open-source. It has its own .7z format which offers superior compression ratio.
ABC (Yet Another Bittorrent Client)
http://pingpong-abc.sourceforge.net/
Is a free, open-source Bittorrent client, you can use it to download files from Bittorrent with is.
Miranda IM
http://www.miranda-im.org/
Free, open-source (GNU GPL), multi-protocol IM (Instant Messanging) client, that you can use to chat with people on Jabber, MSN, ICQ, IRC, etc. It is highly customizable and very easy to use. It is very simple and bloat-free. Doesnt hog your processor power or memory.
DC++ - Your files, your ways, no limits.
http://dcplusplus.sourceforge.net/
Is a free, open-source DC (Direct Connect) client under the GNU GPL that connects to DC hub's for P2P (peer-to-peer) file sharing with other users. Has TTH hashes, etc.
FileZilla
http://filezilla.sourceforge.net/
Is a free, open-source (GNU GPL) FTP client, it is easy to use, it is great, its competly spy/adware free.
Mozilla Firefox
http://www.getfirefox.com/
Great web browser, free, open-source. Secure, safe, tabbed browsing. Can disable Java, Javascript, third-party cookies, third-party loading of images, etc (to get rid of banners), it blocks popups, etc.