Which IPC standard provides land pattern dimensions?
It is in IPC-7351B.  I have the original document, not the "B" version, and the information is in Section 3, Design Requirements.  The dimensions aren't given directly; instead, there are suggested allowances and tolerances depending on the part size, lead shape, etc.  For example, here is a table suggesting how much extra space to give around the component leads:



As you can imagine, it's not easy to use this document, especially when all you want are land patterns :)

I highly recommend using Library Expert.  It packages all of the IPC-7351 recommendations together.  The Lite version is free, and it creates IPC-7351-compliant footprints for a bunch of PCB tools, including Altium, OrCAD, Eagle, etc...

You can tell it which Density Level to uses ("Most", "Nominal", and "Least"). This refers to how much the land patterns will protrude from the actual point of connection.

Please see this earlier answer for more info on Density Levels.

Good luck.