The stock Bridgestone tires on the 2008+ Yamaha WR250R are OK for basic use, but there are definitely much better options out there. Here is our WR250R Tire Guide....
Pirelli MT-21 front tire with Dunlop D606 rear tire
The MT-21's work great on the front of the WR250R and will often go 5000 miles before they need replaced. The D606's work great on the rear of the WR250R. They are best suited for off road use, but their tread compound is engineered for good highway durability and grip. You should get around 3500 miles out of one. Both tires are DOT approved.
NOTE: The Pirelli MT-21 front tire is billed as a 90% off-road / 10% on-road design. If you think you will be riding alot on the street, you might want to consider a Dunlop D606 Front Tire (size 90/90-21) to match the Dunlop D606 in the rear. They seem to work better on the street.
Pirelli MT-43 Trials Tires
Another popular tire setup for the WR250R is to run Pirelli MT-43 Trials Tires front and rear. These DOT legal tires were designed for trials-type riding and competition, but their excellent performance on hard, wet and dry terrain makes them perfect for dual sport use. They provide long-lasting performance, excellent grip on virtually any type of terrain, and are very affordably priced. One side benefit is a tread pattern that has a minimal impact on soil. They can also be run at very low pressures for optimal grip.