i5-520M+ G310M@~RM4k?
Personally I don't think its worth it 
Have you seen the model yourself? The textured designs are unique, not everyone will like it 
Its quite (very) heavy for a 13 incher, but it does have a optical drive...
Based on my experiences, its best to avoid Toshiba models using G310M since they have incompatibility issues which can give you a lot of headache 
The Satellite M500 with the same GPU and weaker processor is already quite hot... I can't imagine how hot the M900 will be because its way smaller 

I would recommend Asus U35Jc~ RM2.6k or the U33Jc (bamboo version)~ RM3.6k. They don't come with optical drives but you could always compromise with an external 1~ The specs are equivalent, if not better than the M900. 

If you just want a light and durable laptop (not capable of gaming), then can take a look at the Portege R700. 

LOL, my previous laptop was a Satellite M100 too haha 
Reliable lappy it is, now in the hands of my sis~ The harman/kardon on that model is quite soft though haha...

Well... you can always buy external speakers for your laptop 
The M900 doesn't come with Harman/kardon. Only a handful of Toshiba units come with those... The newer batch of Harman/kardon speakers are spectacular that I can assure you haha 
Recent Toshiba models that comes with Harman/Kardon: Satellite M500-S432, Qosmio F60-S531/BD533, Satellite M645, Satellite A665 and all the other models of the Qosmio family. I don't really recommend the M500-S432 (touchscreen) since its also using the G310M GPU which causes incompatibility issues that Toshiba hasn't really solved yet...
The Qosmio F60-S531 is priced at around RM 3.2k but its running on i3 only and its 15.6inch in size 
The M645 (RM4k) is 14 inch in size and has a rather powerful processor as well as GPU... but since you don't play games you don't really need it at all...
The A665 and other Qosmios are too large and are out of your budget, unfortunately...

In the end it depends on what you want lo... I would say noneed to spend so much on a laptop with too good specs. Might as well just use the money to buy accessories/ good speakers or something 

LOL.... you definitely want a Toshiba ar? O____O There's many other good laptops from other brands worth considering too...
Still, if it must be Toshiba, then yes, the L635/645/655 are the closest to the M900 in terms of price/performance. They more or less offer the same specs, so it ultimately boils down to what laptop size you prefer (and what color too) haha  The build of this series of laptops are way better than most brands but the specs is quite a bit of a let down... but most Toshiba buyers don't really care anyway haha
I need to warn you that they are rather glossy though... not suitable for hygienic people 

Well.... personally (as an audiophile), the harman/kardon speakers are better (louder too x____x) than cheaper external speakers... you will need to spend at least RM200++ to get really good speakers (I'm assuming you're an audiophile, like me haha  ). You can always head to the Home Entertainment>Audiophiles section in lowyat.net, the sifus there are really pro 

BTW, when will you be getting your laptop?
If its Toshiba then do check out http://www.celebratewithtoshiba.com/
They're giving away free coupons to extend your local warranty to 3 years (worth RM299). The event last until 31 October. 

What bad experience about i3 ?