Frontend:

<config>
    <frontend>
        <events>
            <the_name_of_the_event_to_observe>
                <observers>
                    <namespace_module>
                        <class>namespace_module/observer</class>
                        <method>someMethod</method>
                    </namespace_module>
                </observers>
            </the_name_of_the_event_to_observe>
        </events>
    </frontend>
</config>

Admin:


...

<config>
    <global>
        <blocks>
            <namespace_module>
                <class>Namespace_Module_Block</class>
            </namespace_module>
        </blocks>
    </global>
</config>

EAV:

<config>
    <global>
        <resources>
            <namespace_module_setup>
                <setup>
                    <module>Namespace_Module</module>
                    <class>Mage_Eav_Model_Entity_Setup</class>
                </setup>
            </namespace_module_setup>
        </resources>
    </global>
</config>

Flat:

<config>
    <global>
        <resources>
            <namespace_module_setup>
                <setup>
                    <module>Na...

<config>
    <global>
        <models>
            <namespace_module>
                <class>Namespace_Module_Model</class>
                <resourceModel>namespace_module_resource</resourceModel>
            </namespace_module>
            <namespace_module_resource>
                <class>Namespace_Module_Model_Resource</class>
                <entities>
                    <some_entity>
                        <table>namespace_module_some_entity</table>
                    </some_entity>...

Magento CE 1.6 and PE/EE 1.11 introduced database abstraction, this is the way to set up tables using the new code.

$table = $installer->getConnection()
    ->newTable($installer->getTable('your_module/table_name_in_xml'))
    ->addColumn(
        'entity_id',
        Varien_Db_Ddl_Table::TYPE_INTEGER,
        null,
        array(
            'identity' => true,
            'unsigned' => true,
            'nullable' => false,
            'primary'  => true,
        ),
        'Entity ...

$image = new Varien_Image('/full/fs/path/to/image.jpg');

// you cannot use method chaining with Varien_Image
$image->constrainOnly(false);
$image->keepFrame(true);
// avoid black borders by setting background colour
$image->backgroundColor(array(255,255,255));
$image->keepAspectRatio(true);
$image->resize(216, 139);
$image->save('/full/fs/path/to/save/to.jpg');