Myself, I've always liked Market Leap's slew of tools:
Marketleap Search Engine Marketing Tools
There are a lot of them out there, and I've used just about all of them. SEObook's keyword tool is good, I usually go over to the Adwords keyword tool for a quick check, but since a friend of mine launched KeywordSmash, that's the one I use now.
KeywordSmash! | Access All Your Favorite Web Tools from One Place
The best is keyword elite. I am using it from long time and i haven't found any such problem.
Till now, I could not find a better keyword research tool than google adwords'. Still its the best I believe..
I like Market Samurai, awesome tool. The keyword research tool is free, but loads of tools in the full program.
I also us market samurai and I thinks it is great tool to use.
Try using Google Adwords and couple it with search based google keywords tool.
If you know how to use the Google Trends, then add the analysis of Google Trends to the KW's you have derived or selected from Adwords and Search based google Keywords, and you have killer combination at your hand.
I did it for my clients content, when he asked me to choose the KW's and prepare content for his website. His site was on the first page of google for 3 KW's with 48 hours and he made over $1xxx sale in 12 days...