Tweet Nest by Andy Graulund is rather lovely. It's basically a clean and simple archive of your tweets. Not just the last seven days, but all of them. In order. Searchable. With bar graphs. Unfortunately, creating your Tweet Nest is a bit fiddly-techie – there's lots of talk of PHP and MySQL and other abbreviated gubbins – but hey, it's got bar graphs.
What bugs me is that full archiving isn't already built into Twitter; surely its something most would appreciate? I certainly don't want Twitter to become a lumpen mess like Facebook, with new features thrown in and rearranged every couple of weeks – I just want the existing functionality to work as best as it can.
… and for them to deal with those pesky username-squatters, but that's another story.