Three popular tools:
SpyFu
KeyCompete
Keywordspy
Keep in mind you may find some with very large keyword lists.
Don't think that a competitor with a large keyword list is actually
making money. They may be losing or breaking even. The keyword lists
from competitors should be looked at closely, since many will contain phrases
that you should NOT be bidding on because of their lack of relevancy.
You need to have:
1.) Targeted relevant landing pages that have the keyword in the title
H tags and in the body copy.
2.) Don't bid on broad or phrase match at first - use exact match type only eg. [keyword]
3.) You should be tracking the conversions (thank you page) as well as the keywords to see what converts.
4.) Split test your ads always! Use
Winner Alert.
Adtrackz or a similar program can track the keywords.
Google can track you sales conversions.
Competitive analysis can give you an edge but you need to look at the big picture.
This is probably common knowledge to most of you, but thought it may help someone.
Good luck!
Peace,
O