If you're not planning on spending much, your best bet is this Original Penguin Tunic. It's a great piece, while not very costly. You can also take a look at this Dorothy Perkins Tunic. It's a product you're bound to love which also doesn't cost the earth. You might also want to consider this Halogen Tunic. The price is very reasonable, but the effect on your wardrobe will be pretty fantastic.
If you can afford to spend a little more, why not opt for this Eileen Fisher Tunic. While the price is very reasonable, this product is an easy wardrobe update. It's also worth considering this Tunic. This item is extremely popular and, just as importantly, not very expensive. Consider this Victoria's Secret Tunic too! Great value for your money.
If you're not a thrifty type, then you absolutely must check out this Joie Tunic. This product seems expensive, but it's top quality. While you're at it, also have a look at this ADAM by Adam Lippes Tunic. Yes, this item is expensive, but it does not mean it's not worth it. You can also consider this Alice + Olivia Tunic. You won't regret the money spent!