I have this model:

 

It renders in game, but upsidedown:

 

Model Code:

// Date: 4/6/2014 5:32:28 PM
// Template version 1.1
// Java generated by Techne
// Keep in mind that you still need to fill in some blanks
// - ZeuX
package realmoffera.client.model;

import net.minecraft.client.model.ModelBase;
import net.minecraft.client.model.ModelRenderer;
import net.minecraft.entity.Entity;

public class ModelCoinBagRF extends ModelBase {
//fields
ModelRenderer Shape1;
ModelRenderer Shape2;
ModelRenderer Shape3;
ModelRenderer Shape4;
ModelRenderer Shape6;
ModelRenderer Shape5;

public ModelCoinBagRF() {
	textureWidth = 64;
	textureHeight = 64;
	Shape1 = new ModelRenderer(this, 0, 0);
	Shape1.addBox(0F, 0F, 0F, 16, 10, 16);
	Shape1.setRotationPoint(-8F, 12F, -8F);
	Shape1.setTextureSize(64, 64);
	Shape1.mirror = true;
	setRotation(Shape1, 0F, 0F, 0F);
	Shape2 = new ModelRenderer(this, 0, 26);
	Shape2.addBox(0F, 0F, 0F, 14, 2, 14);
	Shape2.setRotationPoint(-7F, 22F, -7F);
	Shape2.setTextureSize(64, 64);
	Shape2.mirror = true;
	setRotation(Shape2, 0F, 0F, 0F);
	Shape3 = new ModelRenderer(this, 0, 26);
	Shape3.addBox(0F, 0F, 0F, 14, 2, 14);
	Shape3.setRotationPoint(-7F, 10F, -7F);
	Shape3.setTextureSize(64, 64);
	Shape3.mirror = true;
	setRotation(Shape3, 0F, 0F, 0F);
	Shape4 = new ModelRenderer(this, 0, 42);
	Shape4.addBox(0F, 0F, 0F, 4, 2, 4);
	Shape4.setRotationPoint(-2F, 8F, -2F);
	Shape4.setTextureSize(64, 64);
	Shape4.mirror = true;
	setRotation(Shape4, 0F, 0F, 0F);
	Shape6 = new ModelRenderer(this, 0, 48);
	Shape6.addBox(0F, 0F, 0F, 6, 2, 6);
	Shape6.setRotationPoint(-3F, 6F, -3F);
	Shape6.setTextureSize(64, 64);
	Shape6.mirror = true;
	setRotation(Shape6, 0F, 0F, 0F);
	Shape5 = new ModelRenderer(this, 16, 42);
	Shape5.addBox(0F, 0F, 0F, 1, 2, 4);
	Shape5.setRotationPoint(-2F, 8F, 1F);
	Shape5.setTextureSize(64, 64);
	Shape5.mirror = true;
	setRotation(Shape5, 0F, -0.7853982F, 0F);
}

public void render(Entity entity, float f, float f1, float f2, float f3, float f4, float f5) {
	super.render(entity, f, f1, f2, f3, f4, f5);
	setRotationAngles(f, f1, f2, f3, f4, f5, entity);
	Shape1.render(f5);
	Shape2.render(f5);
	Shape3.render(f5);
	Shape4.render(f5);
	Shape6.render(f5);
	Shape5.render(f5);
}

private void setRotation(ModelRenderer model, float x, float y, float z) {
	model.rotateAngleX = x;
	model.rotateAngleY = y;
	model.rotateAngleZ = z;
}

public void setRotationAngles(float f, float f1, float f2, float f3, float f4, float f5, Entity entity) {
	super.setRotationAngles(f, f1, f2, f3, f4, f5, entity);
}
}

GL11.glRotated(180, 0, 0, 0);

This screws up the rendering a little bit:

 

Render Code:

package realmoffera.client.render;

import net.minecraft.client.renderer.entity.Render;
import net.minecraft.entity.Entity;
import net.minecraft.util.ResourceLocation;

import org.lwjgl.opengl.GL11;

import realmoffera.UtilRF;
import realmoffera.client.model.ModelCoinBagRF;
import realmoffera.entity.EntityCoinBagRF;

public class RenderCoinBagRF extends Render {
public static final ResourceLocation TEX = UtilRF.newResource("textures/entity/coinBag.png");
public static final ModelCoinBagRF model = new ModelCoinBagRF();

public RenderCoinBagRF() {
	super();
}

@Override
public void doRender(Entity entity, double x, double y, double z, float yaw, float partialTick) {
	GL11.glPushMatrix();
	GL11.glTranslated(x, y, z);
	GL11.glScalef(0.5F, 0.5F, 0.5F);
	GL11.glRotated(180, 0, 0, 0);
	bindTexture(getEntityTexture(entity));
	model.render(entity, 0, 0, 0, 0, 0, 0.0625F);
	GL11.glPopMatrix();
}

@Override
protected ResourceLocation getEntityTexture(Entity e) {
	return TEX;
}
}

First translate to the center of your model. Then, scale the model if needed. Then...

You want to rotate about either the X or Z axis by 180 or pi.

Then translate back to the original position

Replace

GL11.glRotatef(180, 0, 0, 0);

with

GL11.glRotatef(180, 0, 0, 1);