Hi Lisa,
We are in the middle of potty training. We started with a baby bjorn kids potty, but after awhile my fiercely independent daughter wanted to sit on the big potty like mama.
At first I tried the little seats that you put on and take off the toilet. That worked fine, other than the hassle of having to take it off and clean it all the time (because they DO get yucky). Then a friend of mine blessed us beyond belief and potty training has been going sooooo much better!!!!!
First, she got us "The Potty Pal" integrated toilet seat.
http://www.amazon.com/Potty-Pal-Standard-Toilet-Seat/dp/B...
It has the kids seat integrated in... so you just flip it down and up as needed.
Then, she bought us the Potty Stool. I LOVE this!!!!!
http://www.amazon.com/Elite-Child-Corporation-TPS-100-Pot...
I know it's bulky and a bit expensive...but I can't tell you how much this has changed toilet training for us. One, my daughter LOVES to go to the potty. (we still have accidents when she is really involved in something) She can climb up onto the potty all by herself, the large safety rails ensure she doesn't fall, and it just makes everything SO much easier! No bending over for me to get her on and off the potty. She does it herself. And like I said, my daughter is very independent... and WANTS to do things on her own. So, this opened up a whole new world of independence for her!
I think these are great investments because 1) their butts are going to be smaller then ours for quite some time. So, making it more comfortable for them to go on the potty is great. 2) providing tools that allow them to do this on their own, just enforces the idea that this is a 'big kid' thing and not a baby thing. Baby's need mama's help with everything. Big kids can do things on their own. :-)
So, that's our experience. Oh, and my daughter is just 20 months. So, even though she is younger then a lot of kids when they train, she can still use these items with no issue. I will say, she did have to 'practice' for about 30 minutes (her choice, not mine) when we first received these items. At first she didn't have the mechanics of getting on and off the toilet quite right. But, after her practice session, she's been good to go.
Good luck! Potty training is an adventure!