Like the Caped Crusader’s utility belt, the Internet seems to hold an infinite variety of tools and gadgets that you can easily use through your browser. While an exhaustive list would just be the Google search results for "web utilities", here are a few examples I find particularly interesting and/or useful.

This site offers a several standard IP tools like Traceroute, Whois, and NSLookup all in one place.  Conveniently, the default “Express” option automatically does a traceroute, a DNS lookup, a Whois lookup on the DNS host, and a Whois on the specified IP address.  This is really handy if you have trouble with these kind of functions behind a firewall. Network Tools
In addition to having a number of “lookup” tools like the previous example, provides several port scanners that let you check how good your firewall is.  Be sure to read the "Attention" note at the bottom. IP Port Scanner
Of HP’s 10c series calculators, only the 12c is still being sold almost 30 years after its introduction.   If you want a classic Financial calculator (but don't have $70 to spend on one) the 12c has been well emulated at this Brazilian site.  Incidentally, emulators for other HP calculators - like the 15c and 16c - are also available on this site.

HP 12c Emulator

All HP Calc Emulators

With all the major Google products like Streetview, Chrome, and Gmail, the really simple stuff can be easily overlooked. Within Google search there are certain fact-based queries that return "rich answers" without linking anywhere.  Stock quotes, weather, sports scores, unit conversion, and census data are a few of the things you get by just typing key words and hitting Enter.  For example, if you're hungry try: “1611526157 to hex”.

Google Rich Answers

Calculations Cheat Sheet

General Cheat Sheet

Static. That’s all it is. But it’s amazing how many uses such true randomness can have. Most stuff from is free and really handy when you need random numbers, strings, dates, locations, prices, sequences, etc., etc.... Randomness
I suppose there are some legitimate reasons people distribute unprintable PDF files - the file is all over the Internet, but they can’t stand the idea of it ending up on paper... hmmm... I suspect, however, that many people just check the wrong box before saving their pdf document.  Assuming the contents aren’t confidential, this service will fix that type of file. PDF Unlocker