Telekom's Streamyx service is by far the most common broadband option in Malaysia. Quality ranges from abysmal to quite decent depending on various factors (e.g., location, physical phone line condition, time of day). It is available in most cities.
As of this writing, the following packages are available for residential users:
Any DSL modem you buy in Malaysia will work with Streamyx - but confirm with the vendor to be sure.
The modems provided to customers who choose to rent from Telekom, tend to be horrid. They are from strange unknown manufacturers (they switch brands every few months), and many people find them highly unreliable.