I use WiiMC once in a while to stream music to my home theater, mostly because it handles FLAC fairly well, is compatible with SMB, and starts up faster than my HTPC.
You should also give MPlayer CE a try...
Because of its rudimentary/crappy GUI, I thought it was worse than WiiMC...
But it turns out that MPlayer CE can play H.264 files just fine (and even 720p files, at some extent),
where WiiMC stutters/lags a lot or even refuses to play!