PHP is awesome.
WordPress is awesome.
scriptygoddess is awesome.

I didn't know about the $single trick… I've been using $name, which is true if you are viewing a single post (at least, I'm pretty sure it works the same as single… it has so far).

Here are a few other useful variables. If you're wondering where I found these, I just looked at the .htaccess rewrite rules.

$submit == 'Search' (true if you come from a search and there were either 0 matches, or more than 1 match)
$year will be set if the year is set
$monthnum will be set if the month is set
$day will be set if the day is set
$name will be set if the post name is set
$posts will be set if posts are going to be displayed…
$page will be set if you are viewing a specific page of a post

I've used this to generate an H2 according to what you are seeing. You can combine these to figure it out.

Here is what I am currently using on my test blog. $pagetitle is the variable I use to display the H2 as well as part of the TITLE:

if($submit == 'Search'){
$pagetitle = 'Search Results';
} elseif (!$submit && !$posts) {
$pagetitle = 'No Entries Found';
} elseif (!$submit && !$year && !$monthnum && !$day && !$name && $posts){
$pagetitle = 'Tempus Fugit Blog';
} elseif (!$submit && $year && $posts && !$name){
$pagetitle = 'Archives ' . wp_title('»',FALSE);
} elseif ($name && $posts){
$pagetitle = wp_title(",FALSE);
}