There really is no easy answer to that type of question to be honest. Of course most things will sell, but the equation becomes quite tricky when you have to match all of the criteria that will at least give you a chance at a sale with some sort of margin!
If this was easy, then everyone would be doing it. People spend a long time developing a market, and that includes finding the right product/s, the right supplier, listing the product/s effectively, and so on.........
The products you've suggested are among ebay's hottest selling products, so they will sell for sure. What I am saying is that you will have to invest a large amount and be prepared to sell at small margin to make your money on ebay.
It's all going to come down to your budget, the space you have fro storage, the amount of time you have to dedicate to selling and so on..........
Even if you tick all the boxes you need to, the market can always be volatile, especially in this current economic environment, so finding a sure thing is never easy!
I'm personally a big fan of second hand products. If you can talk a good bargain, you can find all sorts of great deals at weekend markets, yard sales, charity shops and so on.
Your outlay will be inexpensive and you have the chance to make far more margin on these types of products than you do selling a Plasma.
You also have to remember that a lot of people are hurting in the hip pocket and are looking for the best value their dollar can deliver, and selling second hand can offer that.
I only tinker with ebay these days, just as a hobby, but when I find myself at a yard sale or something I'll always keep my eye open for easy money. When I do purchase, I never buy anything that I don't think I can make at least 100% on, and even then I will have to think about it.
Car sound is a big one for me, buyers are always looking for good quality car sound.
Yes, this source does mean far more leg work, but your competition is far less. Remember you're not the only one looking for an online supplier.......the other 3 million sellers are also looking!