I know this is a pricey option, but I went ahead and built a Home Theater PC for about $600 (you could do better than that though, I'm sure), and it has an HD-DVD/BD drive in it. I really lean towards HD-DVD since it is cheaper right now, and I just don't see Blu dropping prices for a while.
I think a couple people speculated (or at least asked about) HD-DVD futureproofness and if it will be available in future standalones, and I think so. Most DVD players play
everything: mp3, jpeg, dvd-a, SACD. How many of these features are ever used? SACD and DVD-A didn't really take off, but they are great little bullet points on a box. My understanding is that BD and HD-DVD both use the same laser, and so implementing HD-DVD support in future BD players would be simple and make sense. It might be a while but, well, maybe that will be the time the old HD-DVD player breaks and you need a replacement. Don't see why you wouldn't see some companies with HD-DVD support.
And micro makes an excellent point that you can get both, cause HD-DVD is just
that cheap right now. I love my HD-DVD's, and it's because they are what got me into High Def movies and they are what's kept me into it, first with a format war that made both sides have some awesome sales, and now in death it is lower priced than ever. BD, on the other hand, has always seemed like it really wanted to be expensive if it hadn't been for those meddling kids and their dog, and now that HD-DVD is dead, BD IS really expensive, nearly all the time. Yeah I can get BD for about $15, but that is way too much for me; it just looks cheap compared to the MSRP of $40.
My longwinded two cents.