RocketTheme makes really good looking templates. I highly recommend them if you want a professional Joomla template with a lot of module position, module variation, typography and preset styles, One of their killer features is the Gantry Framwork. It make the configuration so much easier!
They have a lot of cool extensions like RokPad editor, RokFeatureTable, RokStories, RokBox etc. that will make your web site look awesome.
They also make templates for WordPress, Drupal, phpBB3 and Magento.
And if you need any help, they have a great support forum.
Joomlashack makes beautiful Joomla templates. They have one for every type of web sites : business, blog, school, church etc. They even have one for a wedding web site!
They have some cool extensions like LifeStream, ShackSlides, MarkItUp Editor etc. And they also make WordPress templates.
If you need any help they have a great support forum. If you are serious about learning how to use Joomla, check out the Joomlashack University : The easiest, fastest way to learn how to build websites with Joomla.