a few branded parts you might want are
primo/odessey cranks
macniel/fly/odessey/mutiny bars
fit/odessey/macniel/demolition/colony/shadow stem
fly/mutiny/macniel/colony frame
federal/fly/macniel/fit/colony forks
colony/macniel pegs
odessey/dmr pedals
alex/fly/odessey/proper rims
odessey/primo/shadow/proper hubs
PIVOTAL SEAT, a must have on most modern bmx's animal make some good looking posts, although almost all companys make the same post coz there isnt much room for variaton, macniel make one of the nicer seats avaliable but colony and animal make some goood stuff too!
tyres are a picky subject you should look into what type of riding ur doing, the odessey tyres are a good allrounder aswith the animal asm tyre and a few others!
the only thing i can suggest really is to find bmx'ers and see what theyre bmx rides like, take note of handlebar height and frame size, once you know them two figures you'll pretty much be able to build a bike around it or find a cheap complete!!!
just remeber than some frames cost upto and over the 300quid mark sooo for a 300 complete dont expect something with wheels that wnt buckle after a hard session hehe alienation were meant to be good, but they seem to be drilled out and reconstructed hazard rims, they fail epicly! lol