At the moment, the TiVo HD is the only *in production* box that'd do it. There are the Sony DHG-HDD250/500 DVR units, but (a) they're single tuner, (b) they're out of production, and (c) they use analog TVGoS - which is already unreliable in some areas, and when the analog shutoff occurs in '09, guide data will go away completely. There are devices like the new E*/Sling OTA-only DVR that's coming soon, but that just won't do cable at all.
Keep in mind that if you buy the TiVo HD box ($250-300 typically), you still have to get the TiVo service (~$13/mo, or $130/year if you buy a full year of service, I believe). However, I have a (now discontinued, by all accounts) Series3 HD, and am very happy with it - it's absolutely worth it, IMO.