The Joomla! Extensions Directory ™

I cannot get by without Custom Properties -- inevitably there is always an application within each site which simply needs it.
Most recently on a Joomla 1.7 site (yes, there is a version for 1.6/1.7, go to the website, hopefully they'll update here soon), I used Custom Properties to tag some contacts. It does both the base contacts included with Joomla, as well as the very flexible Contacts Enhanced component.
It really makes life easy and the properties and values you assign to each article, contact and other components (it works with several other components), are truly great
Great work, must-have!

This is a super "out-of-the-box" solution for any developer needing a clever well-thought-out solution for making contacts truly functional and feature-rich. In addition to the easy to configure google map and flexible contact form, the Contact Enhanced component easily displays the increasingly popular QR code for mobile devices.
The CE component integrates beautifully as a seamless overlay to the existing contacts and it's integration even extends to compatibility with Custom Properties, so you can go through and easily TAG all of your contacts according to the properties and values you specify in the separately available Custom Properties component. This means that, for example, a medical practice, you can assign attributes to each of the Contact Enhanced contacts with things like "Referrals: From GP, Insurance: Private".
The Contact Enhanced component also features generous main fields with full text editors, enabling the insertion of many of your usual favourites in the SideBar (such as extra photos, etc), or in a Miscellaneous field which can be positioned.
The very smart module should not be forgotten which lists certain contacts which you associate with a given menu item. I place this in the right and it collapses/expands smartly, showing or hiding the contact associated with the particlar menu item, just great.

In sum, it's a flexible and powerful contacts component that fits SO well on all my sites -- one of those must-have components really.