Are you spending the whole 14 days in Malaysia Chocs?
As Liban suggests, YF jabs are not a necessity. Make sure ur hepatitis etc are sorted though.
The drive from KL to Ipoh is nice - lots of nice mountain sides and scenery. Ipoh itself is more famous for food and pretty girls though.
JB (Johor Bahru) is on the tip of the peninsula (borders Singapore) and is a worthwhile trip as well if you want to soak up more culture and cuisine. I guess since u're all the way there you might as well go to Singapore as well. If you are on a budget then a coach will set you back about 25rm (25dhs - its almost 1 to 1 rate from memory) from KL central station all the way to Singapore. Takes about 5-6 hours all up and you get to stop along the way etc depending which company u use. Or if you can spare a little more then Air Asia flies to JB for about 60rm and you can take a taxi across the border to Sg.
If you want a list of things to do in KL pm me ur email and I'll forward you my 'places to visit' list.
Penang is nice, especially its beaches and if you have the time get a flight to east Malaysia and go to places like Sarawak, Sabah - they have a really nice orangutan sanctuary there