Battletech uses 30mm hex bases for their game and they sell pewter bases to use with their minis, but the problem with them is that they have a fairly thick lip around the top edge. (maybe 3mm) The design was so that older mechs that featured a built in stand could be placed inside the lip and then all that'd need to be done is fill in left over ecessed areas.
However as the years have passed a lot of the mech designs have gotten away from using built in bases, particuarly the clan mech designs. Additionally the mechs have gotten a bit larger in scale and as a result a number of the newer designs don't fit inside the lipped base very well. Most people (including myself) have traditionally fixed this issue by filling the entire recessed portion of the lipped base with greenstuff, which takes a fair amount of work and totally sucks when you have a dozen or so bases to fix.
Other upsides are that they are very light, they keep a very sharp edge on the corners and clean up very easily. The pewter hex bases are heavy and have some wickedly thick mold lines on them which are a giant pain to clean up. Plastic slotted bases can be rather weak and have slightly rounded out corners.
Anyways a while back I decided to fix that issue by doing my own base that'd have a flat top. I'd have this printed about 6 months ago but it'd been buried in my modelling box and ignored for a bit. I dug it out last weekend and finally have them molded.
They could be made in black, grey, or white. I'm leaning towards making the black the standard color. They are a good thickness so they are more sturdy than the plastic slotted hex bases and also feature a tab on the underside to help keep it from bowing. (Not an issue given how study they are, but i wasn't sure in the design phase)
I'm looking to start selling these for $1.50 a base.