Twitter promotes a couple companies to buy tweets above the 100k API limit. We use Datasift for our app and it's fairly cheap and painless. Their API has a few

Twitter promotes a couple companies to buy tweets above the 100k API limit. We use Datasift for our app and it's fairly cheap and painless. Their API has a few nice things too like batching. There are options, it looks like if you are going into building a Twitter client and you are not charging for the app, you're going to have a bad time.