What fisheye lens to get for my Canon Rebel XS?

Canon does not make a fisheye for their APS-C sensored lenses.

Tokina makes a 10-17 m fisheye zoom that will fit your camera

http://www.tokinalens.com/products/tokina/atx107afdx-a.html

The "add-on" .35x lens at under $30 is not going to do much when it comes to producing sharp images. Not when a real fisheye costs nearly $1000.

The only fisheye lens made by Canon is for the full frame DSLR's like the 1D and 5D cameras. EF 15mm f/2.8

As the previous poster stated the only real fisheye lens for a crop sensor camera is not made by Canon. As a result the effect will be lessened, I imagine. Sigma makes a 10mm f/2.8 and a 4.5 f/2.8 for your camera.

Here is part of a review from a person also using the Canon 15mm f/2.8 on a 1.6 crop factor Canon: "I now have a lens that provides me quality in macro shots as well as adding extreme distortion depending on the f-stop used and the distance from true angles. The center of the photo is always crisp and accurate, while the outer edge is high in quality and provides the characteristic "wrap" of the subject without the bland black ring that a filter provides. I would recommend this lens to anyone who likes portrait or macro photography and likes shooting in low light, which the open aperture allows with little camera shake being induced."

I've never used a fisheye lens but currently Canon only makes 1 "intentionally distorted" fisheye lens. The Canon 15mm f/2.8 Fisheye and it costs $675 on B&H online. In fact, the cheapest fisheye lens for Canon EOS cameras on that website is $349.

I have no clue about the lens you are looking at though I do know people that bought Opteka lenses for their SLR's and then quickly returned them. It might be something to play around with to see if you even really want that type of lens though considering the cost of the more popularly known lenses.

Here is the shortcut to B&H with the list of fisheye's w/ customer reviews on some:
http://www.bhphotovideo.com/c/search?ci=274&Ns=p_PRICE_2|0&N=4293919666+4294951192+4294185281

You can check out reviews at http://www.dpreview.com and http://www.the-digital-picture.com

Sorry I couldn't be more helpful.

The best fisheye lens for Canon is Canon 15mm but if you can't afford that Optika lens as your link compatible with Canon Rebel XS
http://www.amazon.com/gp/redirect.html?ie=UTF8&location=http%3A%2F%2Fwww.amazon.com%2Fs%3Fie%3DUTF8%26ref%255F%3Dnb%255Fss%26field-keywords%3Dcanon%2520fisheye%2520lens%26url%3Dsearch-alias%253Delectronics&tag=computer0bd-20&linkCode=ur2&camp=1789&creative=390957

http://www.amazon.com/s/ref=nb_ss?url=search-alias%3Delectronics&field-keywords=canon+fisheye+lens&x=1&y=20?tag-dcmb-20