I have used the Sybex e-trainer that comes with Todd Lammle's CCNA Book. Save yourself some money and DO NOT use e-trainer! That software is a piece of garbage, it does not even support some of the commands that it lists in the labs of its own manual!
Todd Lammle's book is the way to go though. I passed on the first attempt, with a very comfortable margin.
The RouterSim product seems like a more advanced e-trainer, but since e-trainer was such a piece of trash, I shall not buy RouterSim. I also severely dislike their authorization diskette policy (for example, they restrict you from installing the software on your home machine and your work machine.) While I am against software piracy, you should be able to install your legally purchased software as you please, so long as there is not more than one instance running at a time. I will not purchase from them just because of that.