Nirvana 2 is a very good online web GTD application, it is for me one of the best designed/looking GTD web apps that’s available now. The best way I could describe it would be it’s similar to ‘Things’ on the Mac. It’s currently free whilst in Beta.
The major sticking point for many users was its lack of a dedicated mobile application, the HTML mobile version of the site just didn’t do the web app justice.
To remedy this the developers (PeopleLikeUs) have created a dedicated mobile app (iPhone only for now) that is currently awaiting Apple App store approval. There are a few minor sticking points that have caused some extra delays with approval with Apple, but the Dev’s hope to have this sorted soon!
For more details check out the Nirvana blog post.