I think what f&b is saying is that the weak base used to convert cocaine to crack is sodium bicarbonate (baking soda).
The reaction equation would look like this:
Cocaine-HCl + NaHCO3 --> Cocaine + H2CO3 + NaCl
H2CO3 --> H2O + CO2
Basically, sodium bicarbonate (NaHCO3) acts as a weak base, stripping the acidic proton off of cocaine HCl. This generates carbonic acid (H2CO3, the same stuff that is the carbonation in soda-pop), which spontaneously rearranges to a molecule of water (H2O) and a molecule of carbon dioxide (CO2). The NaCl is just table salt, and is generated as a relatively harmless side product of the reaction when using baking soda.
The general case of creating freebase cocaine can be performed with any base. Often ammonia is used. I don't intend to start some kind of pedantic war here, like would happen on Other Drugs, but crack and freebase are really the same thing. The former has the reputation of being more diluted and ghetto, the latter has the reputation of being explosive.
Freebase cocaine, in whatever form, is less polar than regular Cocaine HCl. This accounts for its lower boiling point, which makes it smokable. It also explains why it is far more soluble in nonpolar solvents, like ether. Certain individuals in the past (I hear John Belushi was one of them), used to use diethyl ether to dissolve the freebase cocaine. Ether happens to be extremely volatile, and considering most freebasers do this over the stove, while already high, you can see how explosions would happen.
Now to your original question. Pretty much any non-polar solvent will work for dissolving the freebase. A good option, which is recommended by David Lee, author of the Cocaine Handbook, is petroleum either. It has similar physical and solubility properties to regular diethyl ether, but is chemically unrelated. It is slightly safer. But really, the biggest thing is, don't do it over a stove while high. I'm not sure why certain people prefer to freebase with a solvent, as the product will drop out of an aqueous solution anyway. Does it aid in purity? Maybe someone can answer this. Freebasing has never been my thing. I do know that putting the cocaine HCl in ammonia works reasonably well, and allows you to completely avoid any risk of fire.