I haven't found any good sites for builds. In addition to playing SP and MP, I've learned a lot watching videos of matches and noting people's builds, e.g.,
http://www.youtube.com/user/TehGodlyPerfection?feature=watch
Among all of the many, many build possibilities, a few builds seem common this patch. For multiplayer, I've played or experimented with:
1) The cookie cutter multiplayer build this patch has dual USG-23 gatling guns, dual Strekoza battle rifles (or Lotus - specialized for range have quite a reach), UHR-23 Asanol flash rockets, and Hvy Reverse Joint Putuo legs for stability/firing rate.
2) Pulse cannon tank build. Tanks seem the best counter to the cookie cutter USG-23 gatling gun build. I've experimented with: (Head)HD-19 CHROMEYE, (Core)JOTUN CR113-2, (Arms) UAM-10 SEVERN, (Legs) ULG-92 VINDHYA, (FCS)KV-1T2/OTKRYT, (Generator) SONNE GNE530, (FCS)URD-36/ER, (RArm)UPC-37 / H, (LArm) KO-8K3/KORZINA, (RHanger) KO-2H6/STREKOZA, (LHanger)LOTUS BR429, (Shoulders)PESTWURZ VM108. Vertical rockets can be quite nasty.
3) Godly Perfection's high mobility dual sniper build. I haven't seen anything faster and I've gotten addicted to its speed and mobility. Takes a lot of skill to take on gatling gun builds with it, but it's so much fun to play. (Head) KT-1G/FUXI, (Core)WODAN CR110, (Arms)UAM-23 ANIMAS, (Legs), ULG-20 / L, (FCS)PREDIRE FCS190, (Generator) UGN-71/Lw, (Booster) BT-21 SHINATSU, (Recon) URD-36/ER, (LArm)SEIDENBAUM SR13, (RArm)SEIDENBAUM SR13, (Shoulders)USC-1 DHANBAD. Dual subcomputers on the 2 shoulder slot arms help with shooting considerably. Energy goes quickly, helped by moving in scan mode. For a glass cannon build, I prefer dual Seidenbaum's to Seidenbaum+Strekoza.
4) Quad legs with Salem sniper cannon. Haven't optimized this but something like (Head)BEOWULF HD103, (Core)JOTUN CR113-2, (Arms)KT-4S2/SVIR, (Legs)KT-4N2/BELUKHA, (FCS)FCS-07/Lr UZUME, (Generator)KV-3D3/PROCHNYI, (Booster)TEMPETE BT49, (FCS)URD-36/ER, (RArm)USC-26 / H SALEM, (LArm)KO-2H6/STREKOZA, (RHanger)SEIDENBAUM SR13, (Shoulders)PESTWURZ VM108
I'm still exploring options. I've seen a fair number builds with shotguns for CQC, usually KO-3K2. I haven't tried builds with howitzers or heat howitzers, which I understand can be useful in team matches.