That's really up to your budget.. Elka, Pep, Works, ... If you want long travel than you will need long travel a arms and corresponding shocks.. You have a few options but most will depend on your budget..
So banshee in front and 450 in rearYou can keep an eye out fore some used Works shocks. Sometimes they can be had for around 125$ to 200$ depending on condition.. Some have used Banshee front shocks set to the softest setting and say there "ok" but any more than 50$ for a front set of Banshee shocks I hear it isn't worth the $$.??. For the Rear a Good cheap upgrade is a Ltz400 kfx400 400ex some 450's 250r (try to get the newest you can imo) and the liking with Ken Oconner bushings are a great upgrade from stock.. The bushings I think are 20$ and the shocks can be had for around 40$ ..
Thanks very helpful400 or 450 in rear.. Banshee fronts if you don't want to wait for a deal to pop up.. Remember to get the Ken Oconner bushings.. Here is a link.. http://www.kenoconnorracing.com/400EX Shock on a Blaster.html I could be wrong so im not sure about this one but I think the 450r may have a little interference with mounting it because of the resi ?? Someone may chime in that has done the 450 on how it fits up.. Don't buy a 450 rear shock yet till you find out what one and how it fits.. Then when you get used to the Banshee fronts you can sell them and use that $ towards some Works or Elka's ... I am sure there is probably some better deals out there but here are a few to consider..
http://www.ebay.com/itm/Yamaha-Bans...Parts_Accessories&hash=item338cbd9fcb&vxp=mtr
http://www.ebay.com/itm/YAMAHA-BANS...Parts_Accessories&hash=item2ed0ae2051&vxp=mtr
http://www.ebay.com/itm/Honda-400ex...Parts_Accessories&hash=item19eb2e5b2c&vxp=mtr