Rodinal. Sometimes known as the Holy Hot Rod. Boring pic I know, but I like this stuff. I use it for all my B&W film. It's got everything going for it. It's cheap, easy to use and keeps forever. The negs look good too, especially with 120 format FP4. I worked out that I can develop 85 rolls of 35mm or 51 rolls of 120 with this one £9.99 bottle. That's less than 12p a roll for 35mm... Brilliant! It goes right back to the earliest days of film, having been available since 1891, so it must be doing something right, but I guess the older bottles were more photogenic...