Common-mode chokes are useful for the  prevention of electromagnetic interference (EMI) and radio frequency interference (RFI). They pass differential currents, while blocking common-mode currents.
The main ferrite toroid I used to make chokes, is the Jaycar LO1234. These are available locally for an acceptable price. The size of the toroid is 25x15x10 and a pack of 4 will set you back about A$7.00. 
To determine the AL value of the LO1234 I wound 10 turns of 0.2mm wire onto the toroid and measured the inductance with an AADE L/C Meter. The inductance measured was 102.5

µ

H (NOTE: I've measured 6 LO1234 and the measured inductances where 100

µ

± 15%). I use the mini ring core calculator from DL5SWB to calculate the AL value. The AL value of the LO1234 is approx. 1000 nH/N2. Photo 1 shows a test setup of two LO1238.

Photo 1
I then used my VNA to measure the attenuation for a single toroid. Table 1 shows the measured attenuation of one LO-1234. Please note that the tolerance between Toroids can be up to 30%.

Attenuation @ 1.8MHz -20dB

Attenuation @ 3.6MHz -24dB
Attenuation @ 7.1MHz -28dB
Attenuation @14.1MHz -31dB
  Attenuation @21.2MHz -32.5dB

Table 1


Figure 1 shows the measured attenuation with my home-build VNA. This shows rather good properties, which should do well as transmission line transformer (TLT). However the LO1234 is rather small, so its use is limited.

<FIGURE 1>
Figure 1

Jaycar has a bigger brother, LO1238 (Material L15 size 35x21x13). Owen, VK1OD has a nice write up on a 1:1 Guanella Balun using the LO1238.
I then experimented with four toroids and looped RG58C/U three times through. Measuring and adding another set of 4 improved the performance by 3dB and as I had a few more of the LO1234, I added another set of four onto the coax for a total of 12 toroid. Photo 2 shows the choke in its full glory (really three individual chokes).

Photo 2
Measured attenuation of the above choke:

Picture 1

The next table, Table 2 shows a few JAYCAR toroids and the measured/calculated values.

Toroids

Table 2

And here are a few pictures of chokes I've made.
https://picasaweb.google.com/108203673487279554630/RFChokes#6513141847482329650