You don't say where you are, as different products are sold in different places.
There are two ways to go, the powder products and the Liquid concentrates. The postage to ship the liquids is of course greater, but you can sometimes find one of more brands at a local store. Polymax liquid from Kodak, (sold as Liquid dektol in some markets) is great. Ilford Multigrade is very good. The foma liquid version is also good and may be cheaper in europe. ALso in Europe there are a few other brands.
In the US and Canada, the Liquidol sold by Freestyle Has excelent keeping properties.
Dektol is Kodak's Powder, Foma sells a smilar one. Ilford calls theirs Bromophen (sp?) Again in Europe there are a few others .
The third way is to mix from Scratch starting with the D-72 Recipe - but getting raw chmicals is hard to do in some places.