We have a metro map already online, but if you are looking for a transportation map with more than just metro lines, this is the right place. On these maps you can find trams, buses, metros and so on. They are big and with a high resolution, but if you zoom in, you will hopefully be able to find what you are looking for.
Ps: These maps are a bit outdated as have been commented earlier… for up to date maps which should be 100% up to date visit the updated Pest transportation map or the Buda transportation map. If you have questions concerning the public transportation, visit the Budapest forum and ask your question there.
Budapest public transportation map daytime
Budapest public transportation map nighttime
An older public transportation map for Budapest