I'm looking for a simple, easy to use and possibly free diagramming tool for both basic UML diagrams (mainly use case and activity diagrams) and webdesign wireframes. I don't need any complex UML <-> coding functionality (as provided in StarUML or Enterprise Architect and the likes). I have been using Visio for this and have also tried Smartdraw, but am looking for a cheaper and somewhat simpler alternative that also comes with a set of predefined stencils and templates.
This is the list of the UML Tools (Free/Not Free) : http://en.wikipedia.org/wiki/List_of_UML_tools
For web design wireframes I would suggest Balsamiq Mockups - it is great for doing rough sketches, and most of the functionality is available in the free version (you can also get a free license in some cases).
For UML diagrams, you could try using BoUML. It is quite simple yet has lots of features, and provides very nice UML diagrams (plus its free).
Jude Community is a good free UML tool - not sure on the web design part though.
Netbeans has a UML plugin. It can do basic UML-to-code but not for use case and activity diagrams. You can draw those but they will not generate code. It is free.
The Eclipse UML tools project handles all the basics. For cheap/free web design I'd go with Balsamiq Mockups.
If you are using Eclipse or an Eclipse-based IDE then take a look at WireframeSketcher plugin. Everything is in the name.
You'll want to check out Creately.com - its an easy to learn and fast online diagramming tool with excellent support for both UML and wireframes - comes with templates for both UML and web mockups to get to going fast and its pretty simple to get the rest of your team working on it too.
Some samples of the UML diagrams here - http://creately.com/Draw-UML-and-Class-Diagrams-Online
The best I've found for UML is Enterprise Architect from http://www.sparxsystems.com/
For mockups the simplest and easiest to use is Balsamiq.
For a mockup on steroids check out OmniGraffle (OSX Only).
Otherwise power point is surprisingly productive tool to design quick attractive diagrams. Open office Impress is also ok for a free solution.
If you need visualize classes then the class designer built into VS.NET is very quick, attractive and easy to use.
You might want to try out yEd. This free diagram editor is available for MacOS X, Linux, and Windows. You can use it to easily create UML class diagrams, activity diagrams and use case diagrams. Has stunning auto-layout capabilities, and supports many export formats.
Personally, I like yuml.me for UML, class diagrams and activity diagrams and Balsamiq Mockups for screens mockups.
I find plant uml really great..it is based on http://www.websequencediagrams.com but has lot many other features..
You should check yUML (http://yuml.me/). It is a very easy to use online tool for creating and publishing simple UML diagrams.
I used Umbrello UML Modeller for a while before moving to Enterprise Architect. It is not dissimilar to EA - except that it is free, and Linux based.
Umbrello did about all I needed, but runs on Linux and my development environment is Windows. I used it under Windows in a Linux VM running under the free VMWare Player running Ubuntu, keeping the files on a virtual netwok share that was physically on the host. This arrangement was workable and of course entirely free.
There is an ongoing effort to port Umbrello to Windows, and it will apparently build on Cygwin, but runs slowly; IMO you'd be better off using the VM technique.
If you'd like to focus on building you model and not manipulating objects on diagram. You must try Red Koda Community. Check the sequence diagram video, you can see how easy and fast you can use it with the aid of short cut keys.
The most easy to use, best usability. It’s commercial but also has a free Community Edition license for non-commercial use. Feature-wise (depending on the license) it has everything you may need.