Cork bark makes an excellent basking area. Other options are acrylic docks and home made basking areas made with pvc frames.
The best solution for a (relatively) small tank like a 55 gallon is an above tank basking area. These are home made and can be very fancy or very simple (and inexpensive). The really neat thing about them is they let you fill the tank up with more water which give the turt more swimming room and keeps the water healthier. Here are some examples:
http://www.redearslider.com/forum/viewt ... sc&start=0
Be sure your light bulbs shine directly down on the basking area, be sure the turtle can dry off completely - top and bottom - when he/she's basking, and be sure he/she can't escape.
If you need more ideas for a very simple, inexpensive basking area, here's a clever example:
http://www.redearslider.com/forum/viewt ... 984#141984
I'd worry somewhat about a turtle's feet or nails getting caught in the holes in the "egg crate" in that last example.