What bitcoin mining software is easy to use and start mining immediately with a pool & new ASIC boards?
I would argue BitMinter client is the easiest miner. You go to bitminter.com and click the "start engine" button to start it. You may have to go by java.com and install Java if you don't have it already.

Once the window pops up click "devices" -> "probe all ports" in the pulldown menus to detect connected FPGAs and ASICs. Then click the "start engine" button to start mining.

There will be an update soon to support BFL (Butterfly Labs) ASICs.

If you want to mine on Avalon it has a builtin computer with mining software preinstalled.

disclaimer: I am the author of BitMinter client.