For some reason Joomla core has never natively been able to create custom forms - I'm not sure if this is due to it originally (pre-1.5 releases) allowing non-article content types to sit in the usual database tables that comprise your site, or something else... However, for years there have been multiple extensions floating around that could let you create forms out of basic elements, like text, email and file fields.

The most basic use of such extensions would be to get rid of Joomla's too-simple contact form system.  To do just that it seems that today there are a good 4 or 5 extensions sitting in the extensions directory that could help you out, though the more digging you do the more you'll find discrepancies between them.  Choosing the right form extension should be done with a balance of features to look for, such as:

• A highly active and focused extension developer,
• A multitude of fields already supported,
• A large user base,
• Development of the extension with long-term focus; if the extension has been created to allow the developer to just create 1 or 2 forms on his/her website, it may not be able to do more in the future (given that their initial need for it was satisfied).

Back in 2007 I mentioned the release of a new extension called Fabrik - after spending some time comparing notes between a bunch of form components just now I am back in love with it!  You see, Fabrik takes the approach of forms being essential things for application-building - meaning that with Fabrik, you can create forms to not only email somewhere but store in your database which in turn can be displayed as lists through your site - you you can, for example, use it to build things like a custom library listing of books.

Fabrik was around before last year's CCK-in-joomla copycating< began and is interesting in not replacing Joomla's core article content-type but side-stepping it with a flexible system for handling custom content that supports custom theming and additional plug-in support (yes, you can make your own field types).

Already available fields for forms created with Fabrik include; user details, captcha (with recaptcha!), text areas/fields, file uploads, images, database joins and more (including text displays to annotate fields - for 'help' purpose)...

I highly recommend popping over to http://fabrikar.com and checking Fabrik out... Be sure to also pour through their forums to answer any queries you may have before installing/getting started. 

For those new to these extensions, Community Builder is one of the oldest (and possibly most used) Joomla extensions.  It has a plugin system and lets you quickly develop user profiles for logged in members; with custom fields and member lists.  Because its Open Source and how long its been around, there are a ton of plugins to give you google maps of your members, on-going/live (facebook wall-type) listings of member activity on their profiles and more.

Jom Social isn't Open Source.  Its a commercial release from the Malaysian web development firm Azrul Studio.  They're well known for simple blogging and commenting extensions and have recently released Jom Social - which pretty much gives you the same functionality as Community Builder for $100+ but doesn't require must setup/configuration once installed.

There's been discussion in the Joomla forums about this topic before and I think people are most concerned about the lock-in factor of using commercial software plus the question of how integrated JomSocial is to Joomla itself.

Out-of-the-box, Joomla 1.5 has pretty silly error handling pages - for times when a user hits your site to find a page no longer in existence ('404 Not Found') etc... 

Now, if you like to have your error messages presented to site viewers with the same look and feel as your website, a custom page outside of Joomla might be frustrating - every time you change the layout of your site you'll likely want to edit that page and so on.

There's another approach; some semantic URL extensions can actually redirect those errors to particular content within Joomla.  I recommend using JoomSEF - its a weird extension because of the partially-free (ie. non-GPL) license they've released it under, but you can download and install it for free and then make one edit to its code to remove a footer message created with the free version.

With JoomSEF, you can choose a custom 404 message by typing it directly into a field through the extension's admin side or by choosing a menu item already linking to a message page you've created.  Plus, you can keep track of 404 messages to help streamline your site's navigation!

JoomSEF will make managing your site's error pages easy, and it makes it much easier to navigate your site by URL because you have more control over the format of URL writing rules than with Joomla's stock SEF URLs option!