Does anyone have experience with these in regards to what works best? Do the el cheapo ones work just fine or is there something in particular I should be looking for?
FWIW, I went down this route and determined that rather than buy a 12vdc power adapter for my Acer Aspire One netbook it was easier to simply buy another 110vac adapter ($25 on ebay) and mate it to a 12vdc-110vac auto converter.
It's not a fancy schmancy pure sine wave converter either. Just a simple $25 150w 12vdc to 110vac converter that hangs right off the 12vdc lighter plug. I purchased it at Frys Electronics. I can post details of the make/model if that might help you.
As a side benefit, I can still use the spare AC adapter where I might have actual 110vac (home, friends house, hotel, etc.) or plug other things into the AC adapter.
HTH.