I have tried quite a few over the years, and can recommend the evaluation version of DWGSee, available here and one called Free DWG Viewer. I think the latter program is owned by a new company and now available from
The Autodesk one mentioned by Sunspace has some fancy options like rotation, but it is a whopping download and probably overkill for your needs. When I tried it it also “stole” a whole bunch of file associations from the proper programs. I may very well have missed a checkbox during the install, but do beware if you go that route.