Many nationalities do not require a visa for Malaysia for a stay of up to either one or three months depending on their nationality. For the vast majority of casual travellers, a three-month stay should be sufficient for a first poke around the country. If you need longer, do a border run to Thailand or Singapore and re-enter to get another one or three months. When you enter the country you'll be stamped in for a stay of 30 or 90 days and this is referred to as a Social Visit Pass.
If you do need a visa, Malaysia has three main types of visa that may be of interest to tourists visiting the country. A single-entry tourist visa, a multiple-entry tourist visa and a transit visa. The single-entry visa is valid for three months from the date of entry.
Israeli travellers require permission from the Ministry of Home Affairs before a visa will be issued.
For those requiring a longer stay, a multiple-entry visa can be valid for up to twelve months. This must be arranged via a Malaysian diplomatic mission before arrival in Malaysia, and, from what we understand, is primarily issued for governmental and business needs -- not extended beach research. Please refer to the immigration department website for further information.
The transit visa is, well, a transit visa -- issued to allow a person to transit to another country -- and so is unlikely to be of interest to travellers intent on spending time in Malaysia.
Social Visit Passes can be extended, but it is a little bit of a hassle and many opt to do a run to Thailand or Singapore rather than get an extension. You can (in theory) get two extensions of 30 days apiece at a cost of 50 ringgit each time. For more detail, see our piece on getting an extension to your Social Visit Pass.
The Social Visit Pass is for a single entry only. If you leave Malaysia, you'll just be issued another one (depending on your eligibility of course) when you return.
Given how straightforward it is to get a Social Visit Pass, overstaying in Malaysia is frowned upon. The fine is 30 ringgit per day of overstay, though, in theory, arrest is possible.
Malaysia has land crossings with Thailand, Singapore and Indonesia. Social Visit Passes are issued on arrival at any designated international crossing.