UICollectionViewFlowLayout sub-class that creates layout attributes for items so they render like a carousel. The point of view is from the center of the carousel so is suited for lots of items. It also changes its behaviour based on orientation.

CollectionViewCarouselFlowLayout.m

//
//  CollectionViewCarouselFlowLayout.m
//  iP2
//
//  Created by Lee Probert on 07/03/2013.
//
//

#import "CollectionViewCarouselFlowLayout.h"

#define ITEM_SIZE 300.0f
#define ACTIVE_DISTANCE 200
#define ZOOM_FACTOR 0.2
#define PADDING 20
#define MAX_ANGLE 80
#define PERSPECTIVE 1.0/-400

@interface CollectionViewCarouselFlowLayout (){
    
    UIInterfaceOrientation _orientation;
}

-(void)initLayoutProperties;

@end

@implementation CollectionViewCarouselFlowLayout

-(void)prepareLayout {
    
    [super prepareLayout];
    [self initLayoutProperties];
}

-(void)initLayoutProperties {
    
    _orientation = [[UIApplication sharedApplication] statusBarOrientation];
    
    self.itemSize = CGSizeMake(ITEM_SIZE, ITEM_SIZE);
    self.scrollDirection = UIInterfaceOrientationIsPortrait(_orientation)? UICollectionViewScrollDirectionVertical : UICollectionViewScrollDirectionHorizontal;
    self.sectionInset = UIInterfaceOrientationIsPortrait(_orientation)? UIEdgeInsetsMake(0, 200, 0, 200) : UIEdgeInsetsMake(200, 0, 200, 0);
    self.minimumLineSpacing = PADDING;
    self.minimumInteritemSpacing = PADDING;
}

/*
 Rotate in 3D based on position on screen
 */

-(NSArray*)layoutAttributesForElementsInRect:(CGRect)rect {
    
    NSArray* array = [super layoutAttributesForElementsInRect:rect];
    CGRect visibleRect;
    visibleRect.origin = self.collectionView.contentOffset;
    visibleRect.size = self.collectionView.bounds.size;
    
    int debug = 1;
    
    for(UICollectionViewLayoutAttributes* attributes in array) {
        
        if(CGRectIntersectsRect(attributes.frame, rect)){
            
            CGFloat d = UIInterfaceOrientationIsPortrait(_orientation)?
            CGRectGetMidY(visibleRect)-attributes.center.y :
            CGRectGetMidX(visibleRect)-attributes.center.x;
            
            CGFloat w = visibleRect.size.width;
            CGFloat h = visibleRect.size.height;
            
            CGFloat dRatio = UIInterfaceOrientationIsPortrait(_orientation)? d/(h/2) : d/(w/2);
            
            CGFloat angle = MAX_ANGLE*dRatio; // an angle between 0 and MAX_ANGLE based on proximity to center
            CGFloat radians = DEGREES_TO_RADIANS(angle);
            
            debug = 0;
            
            CATransform3D rotationAndPerspectiveTransform = CATransform3DIdentity;
            rotationAndPerspectiveTransform.m34 = PERSPECTIVE;
            
            rotationAndPerspectiveTransform = UIInterfaceOrientationIsPortrait(_orientation)?
            CATransform3DRotate(rotationAndPerspectiveTransform, radians, 1.0f, 0.0f, 0.0f) :
            CATransform3DRotate(rotationAndPerspectiveTransform, radians, 0.0f, 1.0f, 0.0f);
            
            attributes.transform3D = rotationAndPerspectiveTransform;
        }
    }
    
    return array;
}
 

/*
 Scale based on position on screen
 
-(NSArray*)layoutAttributesForElementsInRect:(CGRect)rect {
    
    NSArray* array = [super layoutAttributesForElementsInRect:rect];
    CGRect visibleRect;
    visibleRect.origin = self.collectionView.contentOffset;
    visibleRect.size = self.collectionView.bounds.size;
    
    for(UICollectionViewLayoutAttributes* attributes in array) {
        
        if(CGRectIntersectsRect(attributes.frame, rect)){
            
            CGFloat distance = CGRectGetMidX(visibleRect)-attributes.center.x;
            CGFloat normalizedDistance = distance/ACTIVE_DISTANCE;
            
            if(ABS(distance)<ACTIVE_DISTANCE){
                
                CGFloat zoom = 1+ZOOM_FACTOR*(1-ABS(normalizedDistance));
                 attributes.transform3D = CATransform3DMakeScale(zoom, zoom, 1.0);
                 attributes.zIndex = round(zoom);
            }
        }
    }
    
    return array;
}
*/

-(CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity {
    
    CGFloat offsetAdjustment = MAXFLOAT;
    CGFloat horizontalCenter = proposedContentOffset.x + (CGRectGetWidth(self.collectionView.bounds)/2.0);
    CGFloat verticalCenter = proposedContentOffset.y + (CGRectGetHeight(self.collectionView.bounds)/2.0);
    
    CGRect targetRectHorizontal = CGRectMake(proposedContentOffset.x, 0.0, self.collectionView.bounds.size.width, self.collectionView.bounds.size.height);
    CGRect targetRectVertical = CGRectMake(0.0, proposedContentOffset.y, self.collectionView.bounds.size.width, self.collectionView.bounds.size.height);
    
    NSArray *array  = UIInterfaceOrientationIsPortrait(_orientation)?
    [super layoutAttributesForElementsInRect:targetRectVertical] :
    [super layoutAttributesForElementsInRect:targetRectHorizontal];
    
    for(UICollectionViewLayoutAttributes* layoutAttributes in array) {
        
        CGFloat itemHorizontalCenter = layoutAttributes.center.x;
        CGFloat itemVerticalCenter = layoutAttributes.center.y;
        
        if(UIInterfaceOrientationIsPortrait(_orientation)){
            
            if(ABS(itemVerticalCenter-verticalCenter) < ABS(offsetAdjustment)){
                offsetAdjustment = itemVerticalCenter-verticalCenter;
            }
        }else{
            
            if(ABS(itemHorizontalCenter-horizontalCenter) < ABS(offsetAdjustment)){
                offsetAdjustment = itemHorizontalCenter-horizontalCenter;
            }
        }
        
    }
    
    return UIInterfaceOrientationIsPortrait(_orientation)?
    CGPointMake(proposedContentOffset.x, proposedContentOffset.y+offsetAdjustment) :
    CGPointMake(proposedContentOffset.x+offsetAdjustment, proposedContentOffset.y);
}

- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds {
    
    return YES;
}
@end