If you want to find trains that don't require advance reservation, do as TheDoc says, but also check the 'only local transport' option, which means only the regional services will show up (in increasing order of slowness: IR/RE/RB/S). There's an hourly service with one or two changes (eg in Nuremberg or Augsburg) that takes about 3hrs 40mins. Watch out when you're typing in places names to add an 'e' when there's an umlaut (eg Muenchen) and it'll bring up the right selection. Any journey after 9am weekdays (or any hour at weekends) qualifies for the €21 Bayern-Ticket (unlimited local travel in Bavaria for a day; €28 for 2-5 people), but I'm not sure if that includes a bike ticket too (usually a few euros more - check the ticket machine at the station). Have fun - I shall be that way myself in the next few days, but training it rather than cycling on this occasion (hence my nerdish researches into DeutscheBahn...)
Matthew
PS As a follow-on from Andy's advice, note that they charge a couple of euros more per ticket if you get it from the manned ticket office as opposed to online or at the machine