AuldLangSyne makes your friends list better. Much, much better. It gives it pretty colors, lets you make notes, and remembers information about offline friends.
AuldLangSyne makes great use of modules. All its functions are neatly segmented out and can be disabled independently of one another.
Modules
Info
Remembers information (like level and class) of your friends for display while they are offline.
Handles coloring and formatting of the friends list. The configuration for this display is tag-based, and documentation can be found on the wowace.com wiki.
Note
Write private notes about your friends, guildmates, and ignored people. Also assign notes to anyone at all. Then display these notes when they log in, or in your tooltip when you see them.
Fu
A FuBar plugin to display your friends list and guild. Colors, columns, sort orders, it's all configurable.
Sync
Synchronize the friends lists of all the characters on a realm. Toggleable on a per-character basis, and disabled by default.
Backup
Backup and restore your friends list, in case of mishaps.
Where to get it
Stable releases of AuldLangSyne can be found on WoWInterface
Bleeding edge releases can be found on files.wowace.com