Why do you need a converter box? Does your TV not have an ATSC tuner? Do you have an HDTV? Most DVRs will allow you to watch OTA TV in HD, but you must have an HDTV with either HDMI or component video inputs. If you're using an old CRT with no digital tuner, then you'll be limited to watching in SD, but the DVR will still work.
The models currently in production are the PHD-VRX, the TViX 6620, and the iView/Homeworx DVRs, which are essentially the same hardware but with different firmware. The first two can record two shows at once while letting you watch a recorded program, while the second two have only one tuner and cannot watch old recordings while making new ones.
The discontinued models include the DTVPal/CM-7000Pal (again, same hardware, different firmware) and the CM-7400. The 7400 isn't recommended, because it has a weak tuner and often overheats. ChannelMaster is supposedly coming out with a replacement for the 7400, but nobody knows when it will be released.
Each of these units has its own topic for people to discuss the ins and outs of using them, and you should also check out the DVR comparison topic. We can't advise you further until we know your priorities.