Is there a Simple minimalistic Twitter iPhone application?

Found exactly what you are looking for. It's called SuperPost by, of all people lol,... MySpace. Needless to say, it's free and also can optionally post to Facebook & MySpace simultaneously. It's not too shabby actually.

I like echofon and simplytweet. Both of which you can customize to your taste by disabling most, if not all, of other features.

Weet & Twitterific are the most minimal of everything I have used. Weet is pretty barebones and lightweight, basically the iPhone version of Itsy. I'm a Tweetbot guy, which is a totally awesome app but it sounds like it does way more than you want.