First of all, please keep in mind that I'm a noob. I haven't even had my camera a week yet. I have a Canon Rebel XSi. I was talking to a friend tonight who also owns a Canon Rebel and she suggested that I get a filter. I'm not looking to do anything professionally. I just want to take general pictures of family get togethers, pets & weekend outings. So, what would you guys suggest? Hopefully I've given enough details for suggestions, if not feel free to ask questions.
For weekend outings a circular polarizer can be very handy. I recommend you get one that is Multi-Coated. B+W is what I use, cost/value/quality balance in my opinion. B&H photography or Amazon are good places to get them. A circular polarizer will help reduce glare when taking picture with water in it. Also at times it may help produce slightly more vivid colors in your image. Also, help deepen the blue in the sky.
The image sensor in your camera already has a UV filter in front of it so you don't need a UV filter. In fact, a good UV filter will neither decreases nor increase image quality, but a poor one can hurt image quality. You only want to add glass to your lens that will help improve the image quality. A circular polarizing filter (CPL) can do that by minimising reflections, enhancing the saturation of certain colors, and if used at a 90° side angle to the Sun, it can darken blue skies. It works best when the Sun is no more than 30° above the horizon which means in the morning and the evening.
Aside from the CP (circular polarizer), the only filters I use any more are Neutral Density (ND) and graduated Neutral Density. A standard ND filter is useful to be able to use a slow shutter speed in bright light (to make running water blur, for example). A graduated ND can be useful when you shoot a landscape to make a smaller exposure difference between the sky and the horizon. http://en.wikipedia.org/wiki/Neutral_density_filter
