There is also http://jetwick.com where you can search your (and also others' !!) tweets. If you searched the first time you probably won't get results for a user. But please ;-), come back 10 minutes later. Then 50 tweets are searchable and stay searchable a long time. What long time is depends how popular you make this service ;-) I.e. if you are using the service regularly you can create a free (!) archive. Again: no payment necessary (this is important for us!). and even no registration at the moment.
There are a lot more features read through the about page (e.g. filter via dates, languages, sort against date, query dependent trends, ...)
There are a lot more features read through the about page (e.g. filter via dates, languages, sort against date, query dependent trends, ...)