Well here's my input for SD DVR's. Others wil give theirs im sure. someone beat me to most of this whilst i was posting but oh well !
You could get another 501 or 508 replacement on eBay - no dvr fee.
You could go for the larger 510, single tuner, more storage, again off eBay - has DVR fee.
you could go for the newer 522/625 dual tuner dual output sd dvr's and pay the dvr fee. Go ebay, dish or one of the sponsors of the site, like dishstore.
Oh! you would also pay another $5 fee if you dont connect it to a phone line.
BTW DVR fees are waived if you get the top packages.
I love my dual tuners, makes watch TV a much better experience, with PIP, record and watch another program. etc. so that would be my recommendation. Also you dont need a HD tv to have a HD DVR, the picture i find better on my SD tv with my HD receiver.