I just finished going through this same debate & ended up getting the Toshiba A30 for $232 from Amazon & am totally satisfied with its upconversion performance ... the ability to play HD-DVD's is just a bonus & I also think you would be best served going with either it or the cheaper A3 which while not quite as good, is still a high quality up-converting player.
The next best choices if you want to save money are (in order of overall quality):
(1)
Oppo 980H at $169 + shipping - This is the best low-end SD-DVD player available, however including shipping costs nearly $200 ... IMO its just not worth it.
(2)
Pioneer DV-400V-K - Doesn't have quite as good IQ or as many tweaking features as the Oppo but is available for $96 at Best Buy & $89 from Amazon.
(3)
Sony DVPNS77H/B - IQ is virtually identical to the Pioneer but offers fewer features & has a few shortcomings for about the same price ... $89 at Best Buy, Circuit City & Amazon.
Out of these three I would go with the Pioneer.