I love LEGO. I hate the Americanism "LEGOS". LEGO is a collective noun. You buy some LEGO; you don't buy some LEGOS.
Picture: Jonathan Stewart
LEGO is the name of the overall toy (and the company that produces it), not of each individual piece. If you want to talk about a single piece of LEGO, you can refer to it as a "LEGO brick" or a "LEGO wheel" or whatever is appropriate.
Need an easy reminder? It's The LEGO Movie, not The LEGOS Movie. The odd plural usage seems well-established in America, but for Australian English it's just flat-out wrong.
A side note: Lifehacker's policy is to always write LEGO with capital letters. LEGO isn't an acronym, but we do this because the company logo is entirely in capitals, and so this looks more familiar. (We follow the same rule for IKEA.)
It would be entirely acceptable to spell LEGO as Lego — it's a company and a proper noun, so it needs an initial capital, but the subsequent capitals are a matter of convention, not an absolute requirement. What matters here is that you choose an approach and stick with it. Accuracy matters.
Lifehacker's Mind Your Language column offers bossy advice on improving your writing.