There are a few on the market. I believe CVA, Traditions, Knight, and T/C all have inline models available.
I have a T/C NewEnglander 12ga I enjoy shooting.
A .62 (20ga) smoothbore flinter can be a good (versatile) choice, too - but price can put a damper on owning one. I had one, but unfortunately the maker cut too many corners in manufacture and it wasn't all that dependable. After the stock cracked and I had it replaced the lock broke. I had it replaced and then traded it before something else broke.