http://www.gramfeed.com, and there are plenty more tools to choose from over the net.
But if you do have an iPad, I highly recommend that you use one of these two great apps:
Podgram - Allows people to view, like and comment on photos just like in Instagram. View your own feed, search photos by tags or location, subscribe to tags, share photos on Facebook, Twitter, Pinterest, Tumblr, and email, or save to Poket for later. You can also easily save photos to your camera roll. What seems like an interesting feature is the ability to print a photo as a postcard, including delivery and billing (using Sincerely) directly from Podgram.
Overall, a useful app that is dead simple to understand.
It still amazes me how the Pinterest layout improves visual content display. Like it or not, it is pretty awesome when other services understand this has proven to be a better way of showcasing visual elements. With this in mind, Pictacular takes Instagram and present it like Pinterest where you can see a larger view of photos with likes and comments. You can do all your Instagram activity same as on the iPhone, with no additional features, just with a real better photo navigation. For example, one thing that bugs me on Instagram today is that you can’t browse pictures scrolling left or right. With Pictacular, you can, and I love it.
The only thing that both services don’t have (nor I could find a service that does it) is the ability to upload pictures from your iPad to Instagram. It is probably something that Instagram themselves won’t allow.