HTPC Optical Drive
If you just want a standard DVD playback, a DVD rewritable drive can be had for around $25 and all do a decent job. Generally Asus
As Blu-ray is now the official standard for HD content, there is no reason to buy a HD drive. If you already have a large collection of HD DVDs, LG makes combo Blu-Ray readers and writers, that also play HD DVDs, such as the LG GGW-H20L Blu-Ray / HD Combo
If you are after a Blu-Ray DVD player, there are a few different types. Just be aware that as Blu-Ray is still new technology, Blu-Ray players are currently quite expensive, and they are constantly bringing out newer, faster and cheaper models. Read more
HTPC Video Card
As mentioned in the motherboard section, onboard video is a great option for a HTPC. Intergrated graphics is quiet, and saves you money. Dedicated video cards can also take up power and create heat, making your HTPC nosier. Dedicated video cards are usually overkill for a HTPC, since a good integrated solution will do the job fine. However if you want to go with a dedicated video card, this page outlines what you need. Read more