“Wait… when did I send that text? I forget when I sent it. I wish there was a way to see that.” There is! With iOS 7, you can easily see the timestamps of all the texts within a message thread.
While looking at a conversation in your text messages, slightly swipe to the left anywhere on the screen to reveal the timestamps of all the messages in the thread.
This is great especially when that person doesn’t respond and you and verify that they got the text yesterday and there’s no reason why they would not respond yet. Sorry… I just revisited some bad memories.