well, a retail card is usually boxed with drivers, software, cables, etc, while bulk/oem is not boxed and you only get the card itself, and nothing else. The oem/bulk will be cheaper, and its fine for most system builders who dont want the 12th copy of windvd from retail boxes...
your choice really, but i would go for the oem/bulk.
i've been using a visiontek 9800 pro 128mb until today (got my new 6800 gt). I did visiontek cuz many of the reviews for this particular card had good overclocking results...i was able to do 432 core and 373 mem 24/7...all i added was actic silver 5 to the gpu heatsink and eventually bought some of the tweak monster ram sinks, which only raised my max mem oc by about 5mhz. My case also has a fan on the side pointed right over the agp slot so i'm sure that helped alot. I basically had a card that was running faster than a stock 9800 xt =). 3dmark 03 scores were around 6500+.....just something to consider if you are wanting a card that will oc well