You can write, compile, run your code online. You can do everything on your browser.
compilr.com - C, C#, C++, Java, JavaScript, Pascal PHP, Python, Ruby, VB
coderun - c#,php, javascript
shiftedit.net - PHP, Ruby, Python, Perl, Java, HTML, CSS and JavaScript
compileonline - wide range of languages
ideone - lots of
cloud-ide - web applications
codeanywhere - HTML, PHP, JavaScript, CSS, and XML
c9.io - cloud9 ide
codepad - wide variety of programming languages
writecodeonline - js php
online-php - php
amyeditor
kodingen
http://spoon.net/eclipse- java
http://ecoder.quintalinda.com
http://ace.ajax.org/ - web
http://edit.orgapage.de - php
http://chpokk.apphb.com/
http://www.landofcode.com/online-code-editor - php
closure-compiler - js (javascript)
HTML, JS, CSS editors
jsfiddle
quackit
htmledit.squarefree
onlinehtmleditor
ckeditor
htmlinstant
timsfreestuff
htmleditor
cssdesk
tryiteditor
jsbin
n2j
of course w3schools - try it yourself editor
SQL Editors
Some of them for to manage your databases (db), others are for trying
dbschemaeditor - db schemaeditor
Execute, try, test your sql queries, your skills.
sqleditor
sqlfiddle
sqlinform
These two are open source. They are at codeplex
sqlwebadmin
sqlwebtools
Demo and trial versions are available
Microsoft SQL Web Data Administrator
cibersql.com
mylittleadmin
sqlwebarchitect
tablesmarteditor