I considered leasing. There are too many issues involved, so I think the best bet is to consult your accountant. Roughly, you might want to lease if you have other business loans, to improve cash flow, or if your total equipment purchases would greatly exceed your section 179 election (this is because the IRS depreciation schedule might be longer than the lease term).
One major difference that many people don't realize between leasing a car and leasing a computer is that computers depreciate at a very rapid rate. A 4-year computer might not have any market value, so payments for leasing or financing a computer for 4 years might have the exactly same monthly payments, if the interest rate is the same. However, you don't get to keep the 4-year old leased computer unless you pay the buy-out amount, but you do get to keep the 4-year old financed computer.