We typically use the following tools for online play:

• Owlbear Rodeo - A simple yet effective virtual tabletop
• Dungeon Scrawl - A dungeon mapping tool that is intuitive and fun
• Donjon Random Dungeon Generator - A tool to create the random dungeon and import it into Dungeon Scrawl
• Token Stamp - A great tool for creating tokens
• Dyson's Dodecahedron - An award winning dungeon designer who shares beautiful maps for free
• Medieval Fantasy City Generator - A tool to create clever maps of settlements and thoughtful districts
• Azgaar's Fantasy Map Generator - A tool for generating whole fantasy worlds which may frankly be overkill