Recently announced, this is looking like the player a lot of people have been waiting for: It's networkable (wired or wireless with your own USB dongle), can be purchased with a pre-installed HD ($259) or add your own ($169), can also connect to external drives via USB, and has good support for HD video formats of all kinds.

I currently use the Western Digital WDTV and I'm very happy, but I might be upgrading to this unit once I hear some reviews.

http://www.mvixusa.com/ultio/1080p-high-definition-home-theater-pc.html

HDD Compatibility
Supports 3.5 SATA hard disk (up to 1.5TB), HDD not included
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HDD Format
FAT32, EXT3 or NTFS format
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External Storage
Via USB Host (for external DVD Drives / Portable HDD / USB storage)
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Video Resolution
H.264, MKV, WMV9, MOV, RM/RMVB, TS and HD Divx - upto 1920x1080p
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TV System Compatibility
PAL, NTSC, Auto
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Networking
LAN RJ45 10/100M or Wi-Fi 802.11N (via USB dongle, not included)
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Network Protocols
Embedded UPnP Client, Samba Client, Samba Server
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Video Playback
Codec: H.264, MKV, WMV9, MPEG 1/2/4, HD Divx , Xvid, FLV, RM/RMVB Container: mkv, ts, m2ts, mts, tp, trp, wmv, Ifo, iso, vob, dat, avi, mpg, mp4, mov, rm, rmvb, divx, xvid, flv {...more...}
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Audio Playback
Codec: MP3, WMA, WAV, OGG, AAC, LPCM, FLAC, AC3 Container: WAV [.wav, .pcm], ADIF, ADTS [.aac], M4A [.m4a], OGG [.ogg], ASF/WMA [.asf, .wma], FLAC [.flac] {...more...}
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Image Playback
JPG, JPEG, BMP, PNG, GIF {...more...}
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Subtitle Playback
sub, smi, ssa, srt, idx + sub {...more...}
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Audio Video Out
Audio Video Out HDMI1.3 (digital video and audio signals), Component (YPbPr), Composite Video output , Optical (5.1Ch Dolby Digital), Stereo audio output (Audio R/L),
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I / O Ports
USB2.0 Host (for connecting external CD ROM / DVD ROM / Portable HDD / USB storage / USB WIFI), USB2.0 Slave to transfer Media from PC. 10/100Mbps Ethernet port (Media Transfer and Sharing across network
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Torrent Client
Embedded Bit torrent Client
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File Management
File Management HDD Format, Copy, Delete, Rename, File Transfer via hand-held Remote
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Power Input
Universal AC 100 ~230V 50Hz, DC
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Power Consumption
Power Consumption DC 12V 2A, 30-W
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Language
Language English, German, Spanish, Italian, French, Portuguese, Dutch, Hebrew