Velvet Blues Update URLs - To find and replace all instances of old URL with your new URL. You can update URLs in posts and pages, excerpts, image attachments, custom fields... etc. Very useful on moving your WordPress Site to a new domain name or any category/tag slug is modified.

Antispam Bee - To block spam comments and trackbacks effectively, without captchas and without sending personal information to third party services.

SyntaxHighlighter Evolved - to highlight the syntax of the source code in more readable format similar to code editors. All most widely used languages are supported.

For a programming blog where code snippets is shared, this plugin I would say is mandatory.

WP-Optimize:

Use this plugin to clean-up your WordPress database tables. It can remove post revisions, trash spam comments, pingbacks, trackbacks, metadata and also optimize your MySQL tables so that it works more efficiently.

Yet Another Related Posts Plugin (YARPP) - The most popular WordPress related posts plugin. It supports both thumbnail and text display of related posts.

Note: This plugin is no longer available.

WP Super Cache or W3 Total Cache Both are caching plugins to improve your site’s page speed score and performance.

W3 Total Cache is the most advanced WordPress caching plugins but needs some technical skills for the configurations.

WP Super Cache is easy to install and easy to use. Along with, you can use Autoptimize plugin for minification and concatenation to optimize HTML, CSS and JS.

MonsterInsights - The best Google Analytics Plugin for WordPress.

It comes with a Google Analytics Dashboard for WordPress that shows you actionable analytics reports right inside your WordPress dashboard. It helps to know exactly how people find and use your website.

Yoast SEO - All-in-one SEO solution for WordPress: