I would first suggest setting a price range you want to look in, and this day in age I would suggest buying used because you can get great guitars for a relatively low price.
If you with with Ibanez (which I also suggest), I would try to find a used RG7620 or RG7621. There are always some on ebay. The only difference is that one has a Lo Pro Edge bridge and the other is hardtail. (If I'm wrong on that being the only difference, please correct me.) I would say don't pay anything over $500, but that may even be a pretty high price to pay. On ebay I see them around $300 and $400.
If you want to go for higher end 7 string Ibanez you have a few to choose from:
The Universe - There are quite a few models avaliable on the used market. UV777BK's are almost always on ebay, and as of late they seem to be going for cheap. UV77MC's are cool but really expensive. If you can find a UV7BK with the green dot inlays at a good price ($500 - $700) that would be the best way to go. They are Universe quality just without the cosmetic details.
Random Others - RG2027, this a cool guitar which people seem to be buying like madmen when one is for sale. The guitar has a peizo in the bridge so you can get an acoustic sound. The RG1077XL is an extended scale length guitar. The neck is longer bascially, I don't remember any numbers though. Anyways, that's a cool guitar and go for around a grand.
ESP also made some cool 7 string guitars. They end with the numbers 307. That's really vague though, so if anyone knows about these feel free to add.
I would recommend any of the guitars above. So this is just my opinion on what I think you should look into. Hope this helps!