Analytics – google.com/analytics/ , about.searchignite.com/uk/ and google.com/doubleclick/ – These range from free to expensive and whilst Google analytics is an excellent free tool it will not track more complex ‘relationships’ such as multiclick attribution.
Webmaster Tools – google.com/webmasters/tools/ – Essential back end tomfollery
Google Global – redflymarketing.com/internet-marketing-tools/google-global/ – allows you to see what Google search results look like in different countries
One stop shop – seomoz.org/cart/purchase_select , raventools.com/ and influencefinder.com/ – A one stop shop with lots of SEO and PPC tools incorporated in the one interface
Link Analysis – majesticseo.com/ , siteexplorer.search.yahoo.com/ and opensiteexplorer.org/ – I LOVE Majestic SEO!
Keyword Research – semrush.com/ , spyfu.com/ , wordtracker.com/ and adwords.google.co.uk/select/KeywordToolExternal – I like the simple things in life hence Google keyword analysis generally does the job
General competitor research -hitwise.com/uk/ – Whilst I’m not a huge fan (I have ‘parted company’ with HitWise in two of the past companies I have headed up!) it is definitely a competitor analysis tool you should consider
Trends/ Insights – google.com/trends and google.com/insights/search/ does what it says on the tin
ToolBars – seomoz.org/seo-toolbar and quirk.biz/searchstatus/ – Nice toolbars for website analysis
Internal link analysis – woorank.com/ and home.snafu.de/tilman/xenulink.html – Catches errors and gives general advice on site fixes