willq - 2:12 am on May 22, 2011 (gmt 0)
The pro SEOmoz tools are well worth the money if you're doing client-based work and can factor the costs into your pricing strategy. I love the LDA tool and keyword difficulty tools in particular (although I wish they'd release an LDA API... it's such a ball ache doing the scores one by one!).
I think what you could use is a mixture of Market Samurai and the SEO Power Suite tools. I tend to use MS a lot during my initial keyword research and then SEO Power Suite for content audits / tech audits and SERPs tracking.
I think they'll set you back a few hundred dollars, but they're one-off fees rather than the monthly subscription.