If it is just a surface stain or blemish, Meg's #39 (Vinyl Cleaner) may work well, especially with a soft brush. It is a dedicated cleaner with no protection, so #40 after would be a good idea.
I've also had very good luck with Soft Scrub. Just make sure it is the kind WITHOUT bleach. I use a wet rag or soft toothbrush, a very small amount of Soft Scrub, and very, very light pressure. It may take a couple of passes, but it will remove a lot of stains other cleaners haven't touched. Be sure to rinse the area with a wet rag several times, and when dry, apply a protectant (#40). This is a very effective way of removing the built up grime in textured vinyl (like door panels).
An all-purpose cleaner may work for you also (like Meg's APC+, simple Green, Orange Blast, etc...). I've found they aren't usually as effective against stain type blemishes as the Soft Scrub.
I have heard very good things about the Mr Clean Magic Eraser, and have even bought one. Unfortunately, I haven't found anything to try it on yet! I go to bed everynight hoping one of my kids will scuff my door panel or something, but it hasn't happened yet. Maybe I trained them too good!
Hope this helps.
Dave