Celcom's 3G Broadband, which is advertised as "unlimited broadband", has a 5GB cap. Dunno whether it is strictly enforced. But the policy is listed on their site, so if you signed up without reading the fine print, then you can't really complain.
Their 'fair usage policy' is laid out over 10 pages using Flash. You cannot copy the text or resize it.
Check it out yourself at:
Look for the 'fair usage policy' link.
I find it amusing that they regard 5GB / month as "extremely high usage". In that case, they should not be advertising it as "unlimited". Here's a screencapt of their policy:
M'sian ISPs' fair usage policies, P1 Wimax gotchas