I like looking at retail stores. Places like Circuit City /Good Guys lower prices for items that have been opened or used. Some of the bigger chains will lower prices for accessories that are no longer sold.
Got a 128 Memory Stick for $30.00. retail $70.00
Got the AC- SQ950 Dual battery charger for $89.00. retail $150.00
Got the Vad-S70 Adapter Ring for $20.00. retail $35.00
Also found a memory stick to floppy disk adapter for $20.00 but the sales person didn't sell it to me. Said the price was wrong. He probably kept it for himself.
Also you can find the Sony Memory Stick Reader/Writer Mouse for $30.00 at some Circuit Citys. Instead of sticking the cord into my camera I just stick the "Stick" into mouse.
All Good Guys/Circuit Citys make their own prices when marking down. The ones outside the bigger cities seem to offer better discounts on certain items because it more difficult to re-sell.
All warranties are still valid on these items. Just make sure you keep your receipts and paperwork.