What poker software is worth it?

OK, I may be ready to capitulate. I have been playing online poker for about 3 years with a modest amount of success. Although I have heard about all the software that can improve your performance, I have thus far dismissed it as either a scam or at best marginally helpful. But after reading several forum threads, it appears that I may be bringing a knife to a gun fight by letting my ego overrule common sense. Please, how about a consensus about which software tools are must haves and give the most bang for the buck?

Search
There are dozens of threads about this. Type 'Pokertracker' or 'PAHUD' into the seach.

Thanks for your quick response. However I must show my ignorance of how to navigate within the forum. How do I get to the search box to be able to access the threads you mention?

Thanks, that's what I was looking for. (And now, belatedly, I see the "Search" option at the top of this Reply to Thread page. Doh!