another vote for the spirit radios.. they are 1-2 watts (2-4 times more powerful than FRS radios) and are on GMRS freqs so you still dont have to reigster a private freq with the FCC.. they are perfect for large construction sites, talking though concrete and steel (large buildings, etc..) and are reasonably affordable (most models are around $200)...
if you need more power or need privacy (private freqs, encryption, scramble, etc..) you will have to step up to "professional" radios..
i have purchased several 4 and 5 watt radios through ebay... you can normally get good p200, p110, sp50, etc.. motorolas for the same price as the spirits (used, but in good condition).. these radios will have more power, better battery life, more privacy, etc.. and will cost about the same amount of money, but will require you to register a frequency with the FCC (i think its about $75 IIRC)
other decent brands include Kenwood, Yaesu, Errickson, and Maxon.. these brands can all be had for a little less than the motorolas usually.. the key is to make sure some radio shop in your area has the ability to program them for you (just about anyone can program a motorola, but not everyone will have the cradles and software for a yaesu)
HTH