I just picked up a Telkom SIM with 1GB data.
No Contract
No landline required.
You can upgrade to a bigger cap anytime.
You can use your own 3g modem (I am using my MTN E270, just use an APN of "internet" without any username or password)
The process took about 10 mins at the Telkomdirect shop in Cresta.
I fall in a "good" coverage area and have been struggling to get any MTN or Vodacom HSDPA reception inside the house even though it works fine outside, so I was a bit skeptical whether Telkom reception would be better.
It definitely is! I get good HSDPA reception with more or less the following speeds:
Ping: 160
D/L: +- 2500kbps
U/L: +- 900kbps
http://www.speedtest.net/result/358050060.png
I am very satisfied with Telkom's offering thus far.