My personal recommendation:

Plants: Petswonderland midvalley, Pet safari IPC
Tanks: Aquascape paradise shah alam (but not much choice if u want curved tanks). Petswonderland great eastern mall for all-in-one tank setup (E.g. fluval edge, fluval spec).
Filters: Petswonderland great eastern mall, Pet safari IPC
Lighting: Fish depot aman suria (apply member got 10% disc)
Fertilizers / conditioners: Petswonderland midvalley, Fish depot aman suria
Aquascaping (rocks, driftwood): aquascape paradise shah alam

For Pet Safari at IPC, got 2 sections. East Aqua occupies a small section in the Pet Safari and they sell plants/fishes/accessories, while Pet Safari themselves sell aquarium accessories as well (near the back). The prices can differ, so be sure to compare the prices if u're getting some accessories.

The ones i didnt mention here dont mean I dont recommend. Just that the above are the shops that I always visit. The pros here might have more suggestions.

IPC is at ikea, used to be known as ikano 

1 utama pet shop only focuses on dogs n cats. No fish stuff there.

up until now, East Aqua Ikano still keep the retarded employee there.
Dunno why they dun just sac him, he contribute nothing.
u go there see him, he either just watch his phone or his newspaper don't even bother to serve customer.

I blame, if u not satisfied, stop whining & quit the job.
You can't perform yet you expect more ?
When your teammate can perform well, why can't you ? dun give excuse.

That fella already been there for many years, i went there few years back, pattern same as now.
I still remember i went there buy live stock 2 times, 2 times also he handle it roughly & just throw the pack of fish on the table in front of customer.

Moved next to the IT shop, end of the corner. Same floor I believe.