Conference website with ticket-sales + sponsorship sales with WordPress?

late answer

Another Plugin

As you can read here, WP Event Ticketing is no longer supported, but has someone who took it over and made EventEspresso ¹⁾ out of it. At a first brief look, it seems to be well thought.

PROS: I haven't found one.

CONS:

• Point is, that the plugin adds tons of new tables.
• There're also (afaik) only activation functions to add the table, so they won't disappear on uninstall.
• I also found some stuff like current_user_can('administrator'), which will break if the admin user role was renamed.
• Scripts/Styles are not properly added and currently using admin_print_scripts/styles and wp_footer hooks.
• It doesn't use the WP Error class.
• Doesn't use the WP default interface styles.
• Uses the admin_notices hook instead of adding css-classes for errors and notices.
• It's also non-OOP (fn based),
• has a lot of stuff in the global scope,
• has a lot of loose type checking and is missing tons of basic php stuff (if($v != '')/* do DB queries */ instead of !empty($v) and strict type checking).
• Another serious drawback and also a security concern is, that not a single query is properly prepared, etc...

There's a free Lite version @official WP Repo, as well as a paid one, that starts with $264 for the advanced - full featured - license. If you want to use any of their plugins, be prepaired to pay even more. And yes, you'll have to pay an additional $5/month for subscriptions (seems to be for support). But there are also Non-Profit discounts.

Possible solution

Your best bet would be to use

1. A Plugin that makes use of Custom Post Types, then use something like the RW_Meta_Box class library to add custom fields for seat reservation to the event.
2. Use a DB-option to store all seat numbers (Use the Transients API to clear the entry after the event has expired).
3. Then retrieve the custom field with your seat numbers option during attendee registration and offer only the available seats.

^{1) I'm not affilated.}

I recently created a WordPress site for a conference and I used the following plugins:

• Conference Schedule by Simon Wheatley
• Contact Form 7 + Contact Form to DB Extension to capture abstract submissions (although I never found an answer to my StackExchange question about how to capture dynamically added fields to the form, which would really have been very nice, since academic abstracts can have any number of authors, really, and I didn't want to clutter the form). There was an abstract submission plugin but I can't find it anymore, development stopped around WP 2.8 and it used PHP shorttags, which are not supported by my host, so that was a bust.
• The above-mentioned WP Event Ticketing by 9seeds. It handled PayPal ticket sales, although manual payments were a bit of a pain to capture - we ended up telling people to use the coupon code "MANUAL", which gave a 100% discount if they intended to pay by bank deposit or cheque, but this confused a lot of people. I never used the email attendees function.

However, none of these really served all my needs, and all required some code tweaking.

I recently used http://wpeventticketing.com/ for WDC2011 in October, I didn't look to far in to all the options but I think it can do everything you're looking for.

I'd suggest also using MailChimp for emailing attendees as it is far better than anything I've found to plugin to WordPress.