In my experience the lower abs are the hardest to target and tone. Does any one know of some really great excerises (without using any equipement) to flatten the lower abdominals?

Actually, I've found that leg lifts done while lying on your back will also work the lower abs - Two tonings for the price of one!
(Two-toned exercise? )

PS - Horizontal arms exercises (while standing - vertical while on your back) also tone the upper abs.
It's amazing how some of these things can be multi-purpose!

if you can add weight or resistence to the routine that helps too.

I also do pelvic tilts.. they have helped me tighten up a bit.

Lay on your back, feet on a chair or couch. Place your arms up and touch your shoulders with your hands (I don't like going behind the head.. too much neck danger). Keep your back on the floor and lift your pelvis groin .. tilt it into the air and tighten. Lift as high as you can and sqeeze for a count of 5. Do 10 of these.

Then lift one leg stright up, and repeat 10 times (leg adds resistance). Repeat with the other leg.

All those exercises are great for you rectus abdominus (the six pack) but as i always tell my clients, don't forget the obliques on either side too. Lie on your back, knees bent with hands on shoulders of the same side.

Slowly then curl and try to take the arm over to the opposite side. Repeat with the other arm - these can be done 5 to 10 times.

As always with any exercises, start gently and slowly - if you feel any pain or discomfort then stop immediately.

I found this page with animations of the exercises they want to show you:
abdominal exercises

Hope you like it as much as I did!

Great Site Lucy!

You know, all of those are great for the exercise portion, but if you actually want to see the muscle you have to lower your bodyfat content. No amount of exercise will make them show until that is done.