I've done a number of kits and found them all pretty good.
Unlike with beer kits, with wine kits you really get what you pay for, and if you follow the instructions, it will come out great! No "tweaking" necessary with wine kits at all.
In the $50-70 range, there are Winexpert kits that are pretty good. Not great quality, but you'll get about a $5-7 quality wine. Ok for dinner, but not for discerning wine snobs! These are ready in about 60 days, and will be good for about a year or so before tapering off in quality. Not deep or complex at all, but very drinkable.
In the $100 range, I've had good luck with Cellar Craft and Selection Estates kits. A bit better quality, like a $10-15 bottle of commerical wine, and pretty enjoyable. Again, maybe not for big wine snobs, but really more than good enough. These can age (and improve) for a couple of years. These make nice wines for company and dinner.
In the $150 and up range, there are some awesome kits. They make very nice wines, like in the $20-$25/bottle range and can easily age up to 5 years. In fact, these won't even be really ready for about a year or so and will improve after 1.5 years or so. I've got a couple aging, and these are more complex and take a bit of time to really smooth out.
There are kits for every variety of wine you can think of- from rieslings to big cabernets, and most of them are pretty good. As I said, with wine kits, you really do get what you pay for. The "better" kits have a higher price tag, but you can find decent Winexpert kits for $60 or so. These kits all require a 6 gallon carboy, but otherwise you should have everything you need if you already make beer. You can usually rent a corker from the LHBS, or buy a double-lever corker for around $25.
The kits come with everything except corks and extra campden tablets (for aging, in a "better" kit).
