I asked a similar question the other day and I found that the 2 top choices are WSFTP and FlashFXP. I know I am cheap but i really don't want to spend anything, not even 20 dollars
I still haven't upgraded from coffeecup. I would recommend coffeecup but I have had a lot of problems using it with vista... if you have winXP, coffeecup is decent and free.