Identify the first and last posts on the page

There aren’t any specific conditionals for the first and last posts on a page. You should be able to identify the first post by using something like:

<?php $c = 0; $style='';
if (have_posts()) : while (have_posts()) : the_post();
$c++;
if( $c == 1 ) $style='first';
elseif( $c == get_option( 'posts_per_page' ) ) $style='last';?>
<div <?php post_class($style);?> id="post-<?php the_ID();?>">

which should apply the class .first to the first post only and the class .last to the last post on each page.

@esmi: Will that work for the last page if there are fewer than posts_per_page on the page?

No – it picks up the last post number via the “posts per page” option in Admin/Settings/Reading.

This is TOTALLY UNTESTED, but it might work on short pages:

<?php $c = 0; $style='';
if (have_posts()) : while (have_posts()) : the_post();
  $c++;
  if( $c == 1 ) {
    $style='first';
  } elseif ( $c == $wp_query->post_count ) ) {
    $style='last';?>
  }
  <div <?php post_class($style);?> id="post-<?php the_ID();?>">

Thanks all! I ended up using the count script to get the first post and I found a way to move my end-style out of the lop so it caps of the last post nicely. I am a bit curious to try the code suggested by vtxyzzy though… it seems like that ought to do the trick. Thanks again!

Correct a few mistakes in vtxyzzy’s post

<?php $c = 0; $style=''; if (have_posts()) : while (have_posts()) : the_post(); $c++; if( $c == 1 ) { $style='first'; } elseif ( $c == $wp_query->post_count ) { $style='last'; } ?>
  <div <?php post_class($style);?> id="post-<?php the_ID();?>">

Thanks