@ Pshemax: Winterblade means the 5770 can drive several monitors at once (3), take a look at the ATI site for the blurb.
The HD4870 is slightly faster than the 5770, particulary at higher resolutions and with AA enabled, it can also be found for less but it runs hotter and some can be noisy. Read the customer reviews, or look to the Newegg site: Find your card of choice and see what the Americans say about it before making the decision

I have had a HD4870 (killed it
🙁 ) and have to say the HD5770 really is just a fraction slower, enough to see in a benchmark but not enough to notice during gameplay.
If you can afford it, go for the HD5770, it's cooler and, in my experience, quieter than the HD4870 as well as having DX11 and Eyefinity at its fingertips (and better HD sound).
If you cannot afford the HD5770, you're still a winner, the HD4870 is a cracking card for the money!But be quick, they're selling fast and some units have sold out already.