If you are a UK map user you will understand the title. On both my PC and Windows Mobile devices a favourite application was/is Anquet Maps together with, for street names, Microsoft Autoroute and its device counterpart Pocket Streets. I wanted similar off-line capability for Android and found AlpineQuest and its companion program Mobile Atlas Creator. The free version of AlpineQuest gives you access to two user loaded maps which is OK for a phone with limited memory. As my Xoom has 32GB I paid for AlpineQuest which supports an unlimited number of maps so I have the whole UK at 50k and selected areas at 25K available offline on the Xoom. Using Mobile Atlas Creator Map sources set to "Multimap UK OS map" you can save whatever areas and zoom levels you want for offline use. For 50k I save levels 8 to 14 and for 25K levels 8 to 15.
The one thing missing is a gazetteer to find where places are but you can download the National Public Transport Gazetteer which has OSGB map references for loads of towns and villages and cut it down to contain just placenames, Eastings and Northings. It's saved as four equal sized xls files on my Xoom (for speed of use) and I can look up locations in QuickOffice. As AlpineQuest can display OSGB Eastings and Northings I can find places whose location I don't know fairly easily.
For offline street mapping you have probably already found MapDroyd which uses OpenStreetMap cached for offline use.
The one thing missing is a gazetteer to find where places are but you can download the National Public Transport Gazetteer which has OSGB map references for loads of towns and villages and cut it down to contain just placenames, Eastings and Northings. It's saved as four equal sized xls files on my Xoom (for speed of use) and I can look up locations in QuickOffice. As AlpineQuest can display OSGB Eastings and Northings I can find places whose location I don't know fairly easily.
For offline street mapping you have probably already found MapDroyd which uses OpenStreetMap cached for offline use.