Ive got about 50-60 of these and have tried lots of others. Brands I would avoid are: Sony, Yamaha (Natural sound), Tandberg, Realistic...to my ears they are sub-par.
Many Kenwoods are also pretty lame....If you want one stick to the 9600 or the later "50" Series (7050/8050). Dont bother with the "Nines" or "Elevens". They look stunning...I have several...but are Mediocre performance wise
Top 3 Marantz's are the 2330, 2285 (Not B) and 2325 although you wont find any in your price range. The 2270/2275 are OK but nothing to brag about at all. Avoid the lower end models.
Pioneer 9100 Integrated is very nice. Im sure the 9800 is at least as good BUT will run you more than 600 most likely.
Sansui in your price range I would strongly suggest the EIGHT DELUXE (Not the Eight). Other ones to consider are the 881, 5000x. Many other great ones but not in your price range.
Pioneer receivers: 1010, 939, SX-950, SX-1050 should fit the bill.
Technics - SA-700 or SA-800
Sherwood - 9910A
NIKKO NR1415
Luxman R1070 or R1120. These are great for detail/clarity...you will hear stuff with these that are missing on almost all of the above receivers BUT they are geared more to acoustic or softer music. If you play "congested" Hard Rock you will lose all the detail that separates them from the rest of the pack.
Hope you find this helpful