I agree with whats been said here, adsense is great, BUT never take it for granted as one day they may ban you for "invalid click" etc.
I have tried a few and they all are crap (im from the UK so cant use YPN yet)
The best i found is bidvertiser but they pay ok per click but i rarly get clicks as the ads are not 100% relevant like they was with adsense.
Read the adsense TOS and follow them very carefully as there is aways someone wanted to kick you in the balls (so to speak
)