In-band crosstalk has been widely considered as a major transmission impairment that significantly impacts the BER (Bit Error Rate) performance of lightpaths in circuit-switched all-optical wavelength-routed networks. Such crosstalk usually occurs when multiple lightpaths occupying identical or adjacent wavelengths pass through an optical crossconnect node. Traditional WA (Wavelength Assignment) schemes pay little regard to the physical layer QoS (Quality of Service), and hence cannot provide optimized network performance in practice. In this paper, we propose four crosstalk-aware WA algorithms as variations of the well-known First-Fit, Random-Pick, Most-Used and Least-Used schemes, with the crosstalk factor taken into consideration. Simulation results show that, independent of the network amplifier placement and the traffic, our WA algorithms can successfully suppress the in-band crosstalk throughout the network, and significantly decrease BER blocking rate.