Glorybox is right. If you are ripping to a lossy format then mp3 is the way to go. It is great quality at high bit rates and will work on any player.
Don't use iTunes to rip it as it does not produce high quality mp3s. Again, Glorybox linked to the right rippers.
If you want perfect audio quality you might also consider a lossless format. These give an exact copy of the cd, at about 60% size (about double the best mp3).
The choice here is less clear as they all sound perfect. I use FLAC as this is what my portable supports, and I can also play it on my computer using WinAmp.
If you need something that plays in iTunes or on an iPod then ALAC is what you need. It is a good format, quite simple to decode, making it suitable for portables as it does not drain the battery too much.
Another plus point is that the ALAC decoder is free for any other software maker to use. This means that you could encode to ALAC for now. If you need to use a different format later you can easily find a tool that will automatically convert for you, without going through the hassle of reripping your cds. I know dbPowerAmp currently supports this, and probably many others.