Consider TiVo Premiere
to be the standard by which all other DVRs are judged.
I've been having good success with digital tuner cards and Windows Media Center under Windows 7 and under Windows Vista. If you've already got a PC, it lets you turn it into a very capable DVR for less than $100.
i7-2600K, H70, P8P67-M Pro, 16 GiB, HD7950, SSD, 3 HD, Blu-ray, X-Fi Ti Pro, Antec P182, S75CF, 3007WFP+2001FP, RK-9000BR, MX518
i5-3570K, GeminII-S524, P8Z77-M Pro, 16 GiB, HD7770, SSD, 2 HD, Blu-ray, InifiniTV4, NSK2480, 55" TV; Asus UX32VD