I\'m trying to cluster the Twitter stream. I want to put each tweet to a cluster that talk about the same topic. I tried to cluster the stream using an online clustering algorit
As mentioned in other comments and answers. Using LDA can give good tweet->topic weights.
If these weights are insufficient clustering for your needs you could look at clustering these topic distributions using a clustering algorithm.
While it is training set dependent LDA could easily bundle tweets with stackoverflow, stack-overflow and stack overflow into the same topic. However "my stack of boxes is about to overflow" might instead go into another topic about boxes.
Another example: A tweet with the word Apple could go into a number of different topics (the company, the fruit, New York and others). LDA would look at the other words in the tweet to determine the applicable topics.