When it comes to clustering, nothing better than keyassort.com comes to mind.
Out of 2,900 keywords, clustering at level 3 leaves 500 groups, which is very convenient for avoiding duplicates.
Advantages compared to others:
- One-time price of $30
- Low cost for scraping top search results—essentially you only pay for xmlriver.com limits, which pulls Google data for like $0.30 per 1,000 keywords—pennies…
- Fast speed—nothing is faster than desktop apps, both for checking rankings and clustering.