In my opinion it would be:
Keyword Research- Google KW Tool and Traffic Travis ( Just cause I've had the most experience with TT) - Would really like to try out Keyword Scout and Niche Cracker.
Link Building - I would go for GSA SER , and the Captcha Breaker that he also developed. Although I have heard numerous good things about Licorne, and of course SEnuke, Xrummer, and BM ( Bookmarking Demon) are all also good. Although each has its own benefits , just starting out I personally would urge you to try GSA! ( Affordable and excellent)
Content Spinning - WordAi is very good. Haven't tried anything else but I am more than satisfied with WordAi.
Keeping track of ranking - Numerous free ways to do this, but if you have a lot of sites and want to stay as updated as possible Serp Book is good.
I see a lot of people suggesting SEO Elite... I've never personally tried this but with all the recommendations I'm gonna take a glance at it now.
When doing SEO usually the main goal is getting that number one spot in Google, of course the other search engines are also valuable to be ranked number one in, most people strive to be number one in Google. Of course, if you grab the number one spot in Google, your more than likely doing something right, and will probably have a top five spot in the other major SE's as well. With that said, Google tools will/should be one of your best friends. Google Analytics is a must and the Google KW tool is suitable for your KW research by itself. Google Webmaster Tools is also a great thing to become familiar with. HINT- Don't put more than one site per Google Account - this enables Google to easily find all your sites and although usually you want them to find ( index ) all your content, its best not to link them together in the same account. Reason being if Google happens to decide they don't like your backlinks then they will go ahead and manual review all your sites and you get to sit back and watch all your income go down the toilet. Hence the reason you see everyone saying DO NOT solely rely on Google for your entire income. Try and diversify with some Social Marketing, building a list, content locking, etc etc etc.
Also I feel like its important to say to run GSA and pretty much any linkbuilding software your going to also need multiple proxies and possibly a VPS. Proxies I use anon-proxies.
I should also tell you I am far from a professional and that these are just my opinions of course. With all that said my top 5 would be.
1. GSA with Captcha Breaker
2. Google KW Tool and TT, MNF ( Micro Niche Finder) , Keyword Scout, or Niche Cracker.
3. WordAi
4.SerpBook
5. Google Analytics.
and of course, I love WordPress and all the plugins to help w SEO - Such as AllInOneSeo...
Good luck!
Tim