I'm thinking of getting a new external flash. What are some that everyone uses? Anything special I should look for when searching?
The SB-800 may be overkill, but it would also be a wireless commander for your D50. (So you could get another 800 or a 600 down the road and set them off wirelessly) I'm probably going to get the SB-800 mostly because I don't want to under-do a flash purchase, but also because mine includes the wireless commander in the pop-up flash.
I'll be different. I chose the sb400 because its so small. I leave it on almost all the time and never have to worry about it. It does bounce one way and it covers 18mm. its about $100, so any upgrade to a bigger flash wont be upsetting if I need it in the future.
I think both the sb600 or sb800 are excellent flashes. The main differences between the two are that the sb800 has a higher guide number, it comes with a diffusion dome, has a built in bounce card, and has a couple of manual operation modes that the sb600 doesn't have. If you plan to use multiple flashes, the sb800 can be used as a commander, but the sb600 can't. Personally, I love my sb800. I've got 3 of them and am very happy with them.
Well that too. The diffuser dome is handy and will run $15-20, so that brings the sb600 up to $200. Whether the extra $120 ($140 without the dome) is worth it depends on what you're using it for. I use three and need every bit of power I can get from them when I shoot building interiors for work, so I easily justified the cost.
The only reason to go for the SB-800 over the 600 is to control other flash units with the CLS if it is not built into your camera model- I have 1 SB-800 and 2 SB-600's and they work very well together. From your camera you can use TTL metering and control the flash exposure compensation on each off camera flash unit independently. It is a very nice and user friendly system.