Disks for Sram Rival calipers

I use Shimano 105 ones with mine, no problems so far

Thanks Steve - just wanted to check there wasn't some weird incompatibility

Yep, mine are Tektro on the CX bike.

Just be wary of sizing, some brands make 160/163/165mm rotors, so make sure it's like for like.  Especially with SRAM Post Mount calipers as they sometimes spec the same calipers with or without the conical washers and switch between 160 and 165mm rotors as a result. On my hardtail I've got SRAM Guides and Shimano rotors, which needed shimming with washers under the calipers to fit.

Obviously bikes with Flat mount don't have that issue.

Using Galfer centrelock with mine - pretty much any  160 rotor will do, it's only with bigger sizes/thicknesses where you might have incompatibility

Some of the very cheap Shimano rotors are for resin pads only, they won't be incompatible, just will wear out that bit faster if used with metallic pads.

I have generic clarks ones paired with my Rival calipers. They've been totally fine.

You can get SRAM centreline rotors fairly cheaply if you look around, if you are wanting to keep things in-brand. I don;t think it makes a whopper of a different on a gravel or road bike.