I wrote about Locus in the archived Edge forum. It works great for me, and I've successfully used it with Dingo, Ermine, and Ermine + Link2SD.
I like it because:
-It works great.
-The amount of detail stored for each map is totally customizable (you can select which "zoom levels" to store ahead of time.
-It's fairly easy to get used to using.
-There is help available on-line, if you need it.
- You can select from a whole host of on-line maps to download (Yahoo!, Google, etc.)