Need recommendations on a good flash for nikon D300?

Can't afford a Nikon flash, could you guys help me to choose another one please?)less than $300).

Look for the Metz 58 AF-1 for Nikon… You can probably find it for your budget price. It has been replaced by the newer 58 AF-2 model, so the price has come down. These compare directly to the SB-800, and only lack the extreme zoom range of the SB-900. The are fully iTTL master/slave compatible. The 58 also has a secondary reflector, also called a "wink light", for a little fill when bouncing the main head.

If you can't find a 58 to fit your budget, the next best thing is the Metz 50 AF-1. Guide number of 50 meters, all the bells and whistles of the Nikon models. It will act as a slave to the built in flash controller in your camera, in either iTTL or SU-4 mode. It is more powerful than the SB-600, and cheaper too.

Metz has been making flashes longer than Nikon has… They are very, very good at it.

You can consider Nikon SB-400 AF Speedlight Flash for Nikon Digital SLR Cameras

Compact, lightweight Speedlight unit
18mm angle of coverage with Nikon DX format digital SLR cameras
Bounce capabilities in 4 steps up to 90 degrees; flash shooting distance range from 2 and up to 66 feet
Approximate guide number of 98.4 feet at ISO 200 (at 18mm zoom head setting)
Operates on two AA-size (1.5V) batteries; fast 2.5 second recycling time