The SB-600 might be better for your needs. The biggest extra feature the SB-800 would have on the D50 is that it can act as the commander for the CLS. So my rec. is to get the SB-600 now, then for your second flash get an SB-800. Whats the point of having a comander, if you have no flashes to command.
I'm a newbie to flash photography so I decided to go with the SB600 to save some money (and not get feel frustrated with the learning curve with flash photography - it's much easier to get frustated when a lot of money has been spent I find).
I put the extra %40 I saved by the SB600 instead of the SB800 towards another lens...
When my photography skills develop to the point where I may need to 2 to 3 sources of light in a portable studio setup than I would buy the SB800.
Check out the speedlight forum - it seems like almost 90% of the users there have a SB800...but I couldn't justify the extra $200 (CDN) difference in cost. Sure, it comes with a diffuser dome, a couple of gels and a built-in bounce card - but the diffuser dome is relatively cheap, I'm getting some free gels from Roscoe and the SB800's bounce card is kinda flimsy - I'm gonna use the ol' index card and rubber band trick for bounce flash. The SB800 does have more power (2/3 stop more), takes less time to recycle (<0.5s difference) but has less total number of flashes per charge (140 vs. 200).
Depending on the user, the SB800 would definitely be the better flash of the two...for my use the SB600 more than suits my needs for its planned use as a portable on camera flash (which allows me to bounce light! yay!) For once, I avoided getting sucked into paying more for features that I won't end up using a lot anyhow!
You can use another flash wireless if you have the SB-800 mounted on the D50. If you want to use a single flash wireless, you will need either the SU800 commander, or a camera with commander mode(such as the D70 or D200).
For me, flash is a backup I don't use very often. That's why I bought the SB-600. But if you do use flash a lot, I would recommend the SB-800 if only for the extra power and faster recycling.
I have the SB-600 and I am very pleased with it. The bottom line is if you can afford the SB800 sure then get it if money is an issue the SB600 is a great flash. Like some others stated I opted to get the SB600 so I could also get the Nikkor 50 1.8D. My next purchase will be a Macro system of lens and the SU800/R1-SB200 speedlights which will give me a way to use the SB600 off camera via the SU800. Jim
I started out with SB600. For my next one I got a SB800...and then another SB800. I think the SB600 is a safe way to get your feet wet. However, if you do a lot of flash and a lot of long range or high power flash then the SB800 will be the better choice with its faster recharge and stronger power. Also, if you have plans for another lighting system (strobes, etc.) down the road and want to be able to use these flashes as slaves then the SB600 will have problems with that (doesn't have SU-4). Other than that go for the SB600
I was in the same shoe as you are in January, but finally decide on the SB800 instead of SB600.. why? with the SB600, i will have to buy a diffuser and add some kind of white card to it... which SB800 has! besides, D50 couldn't do wireless, so another plus for sb800...
the only drawback is the price, but i didn't regret it too much, getting great result from sb800... just my 2 cent!