Telephoto lens for a Nikon D50?

I am looking for suggestions on a good telephoto lens to get for my Nikon D50.

I am mainly looking at Nikon and Sigma lenses. Both seem to have 50-200mm and 70-300mm lenses, ranging from affordable to more than I would like to spend. I am just looking for a descent one for my wedding and honeymoon.

I already have a 28-90mm lens that was purchased with the camera.

Looking for suggestions and reasons behind the suggestion.

I wouldn't worry too much about the lens selection for your wedding - I doubt you'll have much opportunity to take pictures :-)
As you've already noticed, the prices go from about $150 to $1600 for a lens in that zoom range. Without an indication of how much you're willing to spend, it's hard to make a recommendation. As a general rule, you'll pay a bit more for a Nikon of the same optical and build quality, but the Nikon will also hold its value much better (if you ever decide to sell) which justifies the extra cost.
For about $300, get a Nikon 70-300 or the 28-200 (and sell the 28-90).
For perhaps a bit more, get a used Nikon 70-210 (these have been discontinued but they're very good for the price.)
For around $700, get the Nikon 18-200 (and sell your 28-90)
On a side note, how often will you use 300mm zoom?! With the 1.5 crop factor of the sensor, that's effectively 450mm. You can forget about using it hand held. If it were me, I'd, put the cash into a better quality lens up to 200mm.

I have a Nikon D70 and all my lenses are Sigma lenses. If I could have afforded the Nikon lenses I would have preferred them. The Sigmas are great and I have been very satisfied with them so far. They are a little bit lighter weight because more of their parts are plastic as opposed to Nikon lenses which have more glass and metal, making them heavier, better quality, and ultimately more expensive. If you can afford Nikon, I would go that route, otherwise, the Sigmas will work great for you.

I'll second the other's post -- I have Canon DSLRs (5D and 20D), but the Sigma lenses are terrific. For a budget, I'd highly recommend the Sigma 70-300mm APO lens (don't get the slighly cheaper non-APO version). It's lightweight, has a decent maximum aperture, and good macro capabilities. Shots done with it are very sharp. I've had mine for 3 years and am very pleased, all for about $220. At f/5.6 and above, it rivals shots from my 70-200mm "L" Canon lens, which cost nearly 8 times as much :)