Biergarten is a favorite of ours. It's a buffet with a good selection of salads (I especially liked the barley salad last trip), hot foods like meatballs, wursts, ham, sauerkraut, red cabbage, schnitzel, sauerbraten, spaetzle, baked chicken, etc. There's not a huge selection of desserts, but the apple strudel with vanilla sauce is so good, you won't want anything else anyway.
One word of warning, the tables are large and seat about 8-10 people. They will seat other groups with you if your group doesn't fill the whole table. We've usually had good experiences with this and have met some pleasant, interesting people, but maybe we're just lucky.