Blog search tools are numerous; most of them are pretty much useless (per my opinion). Here I am looking only at the most helpful and unique ones that I do recommend trying and that offer some great features.

Google Blog SearchTechnoratiBlog PulseBlog Lines
Sort by relevance/ dateonly by datedate or relevancedate / relevance / popularity
Overall results relevance / usefulness highmoderatemoderatemoderate
Most useful advanced search option [inblogtitle] and [intitle]Search for blogs with highest “authority”backlink research operatorSearch for blogs with most subscribers (hence “more popular”)
Subscription options RSS and emailRSSRSSRSS
Most useful additional feature Blog meme trackingRelated tag cloud“Trend this” graphFeed search

Google Blog Search

Google Blog Search is a multi-language, multi-platform blog search engine maintaining the largest index and fastest update rate:

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Technorati

Technorati “indexes more than 1.5 million new blog posts in real time”:

“If Google is the Web’s reference library, Technorati is becoming its coffee house.” [source]

Blog Pulse

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Blog Pulse is a blog search engine and blog buzz tracking service developed by Nielsen BuzzMetrics.

Blog Lines

BlogLines.com was founded back in 2003 and is currently a property of IAC Search & Media (also operating Ask.com).

Two more blog search tools I failed to find helpful enough: