Glad you like our reviews! HDMI out is pretty common on 10" Android tablets, but you won't find DVI unless you can find an HDMI to DVI monitor adapter.
I'd pick the Transformer over the A500 for video playback because the A500 has particular difficulties with 720p and 1080p high profile video. You might want to look at the video review we just posted of the Acer A510 which simply rocks for HD video playback and is on sale for $429 on Amazon right now (just $30 more than the first ten Transformer). The newer Qualcomm dual core tablets and the quad core Tegra 3 tablets handle HD video playback much better than 1st gen Nvidia Tegra 2 dual cores did.
There's also the Asus Transformer Pad TF300, a slightly lower end version of the Transformer Prime that will replace the 1st gen Transformer at the $399 price point. It's not in stores yet, but we'll have a review of the TF300 soon.