Moimeme put some book titiles up but I forget what they are.
I have tried to reduce stress, eat better, plenty of exercise and sleep. I've tried vitamins and fish oil and reading books to help memory. I even tried those Focus Factor vitamins I see advertised. Nothing has helped me except my day planner and lots of post-it notes!
I actually had a minor stroke some years back. I didn't even know it happened until I was talking with some friends and we were talking about our marriage proposals and I realized I have absolutly no memory of my husband proposing. Nothing, zip, zero, zilch. Then I tried to remember other things that my family told me about and I couldn't -- its like they never happened to me. Some memories I can feel in the past -- like I know something happened or was said, but I don't remember what it was. I had a scan done and some other tests and the doctor told me that my brain showed signs of me having at least one small stroke -- maybe several.
If you think your problem is serious - get thee to a doctor. Otherwise there are some mental exercises that you can do to help stimulate the memory process. Believe it or not the doctor told me to play the game Concentration to help exercise my brain. But don't play the same game more than 3 times because then its just random memorization and ceases to be exercise.