I live eat sleep and die by nichebot. It gives me access to google paid search estimated clicks, wordtracker and keyword discovery for under $15 / month. I also find it alot more convenient than keyword discovery and wordtracker.
Jim Morris provides very up to date keyword research data as well. You can check out his blog at:
Beyond keywords, we take keyword research and search engine optimization to the next level by entering the mind of the consumer, it's a treasure trove of data.
I have no affiliation to him and nichebot other than the fact that I am a rabid user. It saves me over $80 / month (cost of wordtracker & keyword discovery) and provides me way more value.
The only other keyword tool that I would suggest is spyfu or keyword discovery.
SpyFu,
keyworddisovery.com. They both take the google paid and natural search data and do some very cool competitive analysis with it. (I don't use them though, not worth my time.)