Falken Azenis RT615s are cheap as hell and not a bad choice. They wear out FAST with track duty tho. They're also prone to getting greasy as they overheat. They're almost cheap enough to offset the fact that they'll wear out in 15-20k miles.
Bridgestone RE-01Rs are a bit better than the Azenis, but at almost twice the cost. They will last a lot longer too. They take longer to warm up tho, but once they hit their operating temp, they are very grippy. They will also get greasy after 5-6 runs tho, so keep a sprayer handy.
I have a set of Dunlop Direzza Sport Z1 Star Specs (long name, huh?) en route to be delivered on Monday. Everything that I've read about this tire is that it outperforms even the RE-01R, and at about 2/3rd the cost. The Star Spec compound is supposed to heat up very, very quickly. Like in 3 or 4 turns. Despite heating up really fast, they maintain temperature very well and don't get greasy as quickly as the Azenis or RE-01R.
A lot of people like the Yokohama AD07s. Yokohama likes em the most tho. I think they're almost twice as much as the Falken and Dunlop.