There are lots of threads discussing nearby alternatives like Augsburg, Landshut, Rosenheim, Tegernsee, Landsberg am Lech, etc.
I'm partial to the Tegernsee area. My brother and I lead a trip to Oktoberfest trip every other year and we spend the first few nights in Tegernsee before heading into the city for the second half of the trip. The lake has several small villages surrounding it which are joined by bus (free if you are staying in the area), a foot/cycle path or ferries. It is close enough to Munich using the BOB train (they have a combo BOB-MVV ticket) that you can go into the city have some fun and come back the same day if needed, also public transportation around the lake is usually included with your hotel. Since it is a touristy area there is a lot of good infrastructure for visitors. There is a great Brewery/Restaurant right on the lake, Bräustüberl Tegernsee. It also beats any areas north of the city in terms of scenery. Last of all room in Bad Wiessee are cheap compared to Munich, last year I've booked a triple room for 99€/night for the first weekend of Oktoberfest.
DJ