You can tell the aircraft type on just about any web based res system, but I don't think you can search by type.

However, here is a list of routes that use the particular type of AC, off the top of my head:

777:
EWR-CDG, FCO, IAH, LGW, MAN, MXP, NRT, TLV

IAH-CDG, FRA, LGW, NRT, EWR

737-800:
EWR-ANU, ATL, BDA, BOS, BUF, CLE, IAH, LAS, LAX, MCO, MHT, MIA, PBI, PTY, ROC, SFO, SJO, SXM, TPA

IAH-ANC, AUS, ORD, CLE, CUN, CZM, DFW, GUA, LAS, MCO, MFE, EWR, PHX, SAL, SAP, SAT, SEA, SJO, SJU, TPA

CLE-IAH, LAS, LAX, EWR, PVR

Feel free to add to my list as I am sure I left stuff out.