There is another promising Twitter client coming to the N900.

It has an interesting concept for the use of landscape mode.

Here are some screenshots.
Landscape Mode


Portrait Mode


The author has made a post about it here

He is also the developper of MoneyFlow and TaskFlow.

At the moment I am using Khweeteur, it works pretty well, the main drawback is that it doesn't show retweets in the timeline but appart from that I like how fast it is. It is a work in progress and lacks a few features but I still prefer it to using web clients.