Rleo is wrong; you can operate a 555 with pin 5 over quite a wide range. But it's not a very ideal VCO - the frequency vs. voltage graph is not linear, and an increasing voltage causes a decreasing frequency (over most of the range, at least). You can improve it by adding external components - see
http://www.electroschematics.com/7170/wide-frequency-range-555-vco/ (I have not tried and don't necessarily endorse that design.)
The 566 is a very old device and appears to be obsolete.
There are many devices that can be used as VCOs. A popular and easy-to-use one is the CD4046B (see
http://www.digikey.com/product-detail/en/CD4046BE/296-2052-5-ND/67295). It is an old device, but is still used, and manufactured by three companies: NXP (formerly Philips), ON Semiconductor (formerly Motorola) and Texas Instruments (who acquired it from National Semiconductor).
Avoid versions of the 4046 that include 74 in the name; most of these require a 5V supply voltage. The 4046 operates from supply voltages up to 15V (some versions can tolerate 18V).
The 4046 WILL be damaged by voltage surges and spikes on the automotive +12V power supply rail; you NEED to include clamping (using a zener diode and/or voltage suppressor with series resistors) and/or an automotive voltage regulator if you're operating ICs in an automotive environment, which is harsh (Google load dump). Regulation is a good idea anyway, since supply voltage variations will affect the VCO behaviour somewhat. Clamping may also be needed on the control voltage, to avoid damaging the high-impedance control voltage input of the 4046.
The 4046 is easy to use as a VCO because it has two auxiliary resistors that can be used to determine the frequency range covered by the full range of control voltages. For example, if your control voltage range is 0~10V, you can set the 4046 to produce a corresponding frequency range of 10~1000 Hz, or 100~200 Hz, or 10,000~10,010 Hz, or 10,000~15,000 Hz, or whatever you need. There is a single timing capacitor (as in most VCOs).
It also has a very high-impedance control voltage input, which is helpful if you want to add filtering on the control signal because it will not cause a voltage offset.
I suggest you get all of the following data sheets, because different manufacturers provide different types of detail:
NXP:
http://www.nxp.com/documents/data_sheet/HEF4046B_CNV.pdf
ON Semi:
http://www.onsemi.com/pub_link/Collateral/MC14046B-D.PDF
Texas Inst.:
http://www.ti.com/lit/ds/symlink/cd4046b.pdf
And buy a few devices and play around with different values for C, R1 and R2 to get the idea of how to use it.
As I said, there are other VCO devices available. Have a look at Digikey's selection table at
http://www.digikey.com/product-search/en?FV=fff40027,fff80205&stock=1&quantity=1&pageSize=250 but beware, most of the options are SMT (surface mount technology). If you filter those out, there aren't many options left; most of those are variants of the 4046.
If you want any more specific advice, you need to tell us more about your project.
