Three strikes laws establish severe penalties for defendants with qualifying prior convictions, even those who aren't charged with a third strike. Under many sentencing schemes, convictions for "serious" or "violent" felonies count as strikes. Determining what, exactly, qualifies as a serious or violent felony requires consulting the three strikes laws in question.
In California, for example, the three strikes laws list the offenses that qualify as serious or violent felonies. (Attempts to commit these crimes also qualify.) In addition, there are many crimes that, while not themselves listed in the three strikes laws, can become strikes because of the way in which defendants commit them (for example, seriously injuring a victim in the course of an assault).
The following is just a sampling of felonies that are "violent," "serious," or both in California:
If you're facing any kind of criminal charge, even if you don't have a felony on your record or aren't currently facing one, you should consult an experienced criminal defense attorney. Only a knowledgeable lawyer can fully advise you of the applicable sentencing laws and adequately protect your rights.