It changes all the time. I'm not trying to push Wilson (all brands are equal quality, imo), but they generally have the best deals in that type of racquet, mostly because they just make more racquets than anyone else. Dunlop usually has some good ones too.
The older model Wilson 6.1 can usually be found at a good price - there are two models, the standard and the "Team". The standard 6.1 is a classic - awesome control, a little heavy (a good thing, imo), 95 sq in, 16x19 string pattern. The Team is lighter, and with a tighter , 18x20 pattern (not as good for spin, but your strings will last quite a bit longer).
Head Radicals can be found at good prices as well - excellent control, fairly flexible. They generally come in two options: midplus and oversized - the oversize is better suited for intermediate players, the midplus is better for advanced players.
It's hard to think of everything off the top of my head - there's just so many good deals to be found. I suggest you just visit a local shop and see what they have. The best deals are just the racquets they have left over from the previous year, that they are selling at reduced prices. If you find something you like, post it here and I'll tell you if it's a good racquet/price - I know what the dealers pay for them, so I can help you bargain with them over the price.