Server Diagnostics & Maintenance

• Pingdom – Monitors HTTP, UDP, TCP, PING : Sends a TXT alert if there is an issue.
• DNSstuff – Comprehensive DNS Diagnostics: Full Analysis Reports, Reverse Lookups, Traceroutes, Ping, SPF, Whois, and way to many services to list.
• Netcraft – Provides Host Netblocks, Application/Web Server make/model, sub-domains, provides a historical list of changes to Servers/IPs overime.
• Charles – AN / HTTP Proxy, HTTP Monitor/Reverse Proxy that allows you to view and record all of the HTTP traffic between a client machine and the Internet. This includes requests, responses and the HTTP headers (which contain the cookies and caching information).

Web Development Diagnostic Tools

• Firefox Firebug Extension – With Firebug you can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.  Its insane, just download it.
• Firefox YSlow Extension - YSlow analyzes web pages and tells you why they’re slow based on the the book High Performance Web Sites: Essential Knowledge for Front-End Engineers which you can purchase from Amazon. YSlow is integrated with the Firebug.
• Firefox Web Developer Extension – Since FF became popular amongst developers this became the de-facto tool for front-end  engineers and designers to figure out “how to make web pages appear correct” in various browsers.  The extension adds a menu and a toolbar to the browser with features that allow you to accomplish the above goals of getting your designs to look A+.
• Firefox Server Spy Extension – Its another great tool that indicates what brand of HTTP server you are accessing (e.g. Apache, IIS, Sun-ONE-Web-Server, Tomcat, IBM HTTP etc.)
• Browsershots - Makes screenshots of a web page in a variety of different browsers running on a plethora of operating systems.  In total, it has the ability to produce screen shots [for design/layout debugging] on roughly 80 variants of browsers/operating systems.

Security Analysis Tools

• HTTPPrint - httprint is a web server fingerprinting tool that relies on web server characteristics to accurately identify web servers, despite the fact that they may have been obfuscated.  httprint can successfully identify the underlying web server when their headers are mangled by either patching or other methods.
• ISAPI_Rewrite – Is a powerful regular-expressions-based URL rewriter for IIS. It is compatible with Apache mod_rewrite  (in fact it will interpret Apache mod_rewrite .htaccess files, so you can change web servers w/o any hassle).
• ServerMask – This is an add-on for IIS which masks the brand of your server by modifying its HTTP header data as well as modifies your web server’s “fingerprint” by removing unnecessary HTTP response data, modifying cookie values, removing the need to serve file extensions, and adjusting other response information.  If curious, you’ll have to try httpprint against a production copy of ServerMask to determine its accuracy.

Software Development & Lifecycle

• FogBugz – Is a simple to use bug tracking system.  In addition to tracking, prioritizing, and coordinating bugs and issues.  It can also be used as project management software to better coordinate team communication.
• Atlassian JIRA – In a nutshell JIRA is the most robust bug and issue tracking as well as project management software on the market.  
• Atlassian Bamboo – Is a Continuous Integration and Build Server.  It automates the process of compiling and testing source code, saving time and instantly alerting you of build issues.
• Subversion – Is a widely-used open source version control system.  It maintains current and historical versions of files [typically source code and documentation].
• Versions – Is a new [just out of beta] Subversion client of OS X.  Its amazing, just download it now!

Database Design / Management / Monitoring

• Sybase PowerDesigner – By far the most robust data modeling tool.   Designing schema’s, physical data models, reverse engineering databases, the list is endless.  But save now, its $$$.
• Red Gate SQL Prompt – SQL Server code completion of database object names, syntax, and snippets as you write, intelligently offering only appropriate code choices.  If you write a lot of DB code or work with various databases intelligent name retrieval saves hours.
• Red Gate SQL Compare – compare and synchronize SQL database schemas, automatically traverses all objects and gives a full report prior to providing options for synchronization or simply providing a synchronization script to run at your leisure.
• Red Gate Data Compare – similar to SQL Compare with the caveat that it compares the contents of two databases and automatically synchronizes your data.
• Red Gate SQL Data Generator - One-Click realistic data generation based on the column types you specify. 
• Navicat for MySQL – Best GUI for MySQL database administration.  Distributed for Windows, OS X, and Linux.
• Navicat for Oracle – Just released two weeks ago.  Compatible with oracle 8i to current and supports all objects including directory, tablespace, synonym, materialized view, trigger, sequence, type and more. **Really looking forward to spending more time reviewing this product.

Of course this list isn’t complete, but hopefully you are able to integrate some new tools into your life. Also, please comment if you have any suggestions of items I’ve missed.