What type of riding do you do and what is your local dirt like? Tires can range from low preformace but long lasting to high performace and medium lasting. Possible ones that I suggest are:
Rear:
Kenda Millville 120 x 19 (this the tire I run. Combined with the millville front it made my KX500 handle and corner like no other combination I have ever tried - my area is single track, sandy loam. and clay. I run these on my 450 now. Very long lasting for single track. I have an indepth review somewhere if you search.
Maxxis IT - A heavy tire. I have never tried these but they are the most popular tire in my area, offer good performance and are probably the most long lasting tires other than the M5B.
Maxxis SI - Nice looking tire. Stiff carcass-meaning may not flex well. I have one on my wifes bike. Seems to work very well but It is a low hp bike so not a good test. Wider spaced knobs than the IT so would be better in loam.
Dunlop 756 - 110x19 Was stock on my 450. A very good performing tire but had a short, short life and lost all traction when worn.
Dunlop 952 - Never tried but similar to the old 752 which was excellent. The 752 had a very short life on my K5 (bald in one day in rocks). The 952 is suppossed to be much tougher.
Front:
I tried a number for front tires on my K5.
Stock Dunlop 490 - ugh! Ran it for a few years. Double ugh.
Dunlop 755F - felt good until it rained. Then I was on my face every corner. Took it off right away and gave it away.
Dunlop 745F - Stock 450 tire. Is generally ok but slides bigtime in any slippery stuff. I put it on my wifes bike.
Kenda Millville - Putting this on the K5 was a cornering transformation. I have a deeply rutted clay road on my trails and after a rain you can play in ruts, hopping from one to another at ease. None of the other tires would do this.
If you want top tire performance I would recommend the Millville 120 rear. If you are not as interrested in super performance as longevity, then the Maxxis IT would be the one. remember that these are only opinions and will vary based on your ridding terrain, type and personal preference. I skipped Michelins in this since in my area they are 2x the cost. Cam.