Royalist sources predominate for Brentford.  The most useful are:
Ashmole MS830 fo. 292 (in the Bodleian Library):  This is reprinted in Turner’s History of Brentford (1922) (though the folio reference is wrong) and in the English Historical Review Vol 36 (1921).   This is a letter from M.S. (probably Matthew Smallwood) who was serving with Sir Edward Fitton’s (royalist) regiment which was involved in the assault on Brentford.
John Gwyn’s Memoirs:  Gwyn was a soldier in Sir Thomas Salisbury’s (royalist) regiment of foot and appears to be the primary source for the attack on Sir Richard Wynn’s house.
Historical Manuscripts Commission:  Calendar of the Marquess of Ormonde:  This provides John Belasyse’s (royalist) account and gives interesting detail on the latter stages of Brentford, Turnham Green and the retreat.  Belasyse was a royalist regimental commander who had commanded a brigade at Edgehill.

Cornwall Record Office DDT (Tremayne of Heligan) 1609/1:  a letter quoting Lord Mohun, who was with the royalist forces at Brentford (by accident). It is dated 19 November 1642 and contains some interesting details.
Peter Young’s Edgehill: is useful for its reprint of some of the relevant contemporary (royalist) accounts including ones from Sir Richard Bulstrode’s Memoirs and Reflections (1721) - Bulstrode served in the Prince of Wales’ (royalist) regiment of foot; Prince Rupert’s ’Diary’; and some extant royalist pay warrants from 16 and 18 November 1642.   
 
Clarendon is always useful and the royalist ordnance papers (Roy) provide the detail on replenishing the royal army with powder and shot prior to the assault on Brentford.

Parliamentarian accounts include:

Historical Manuscripts Commission 29th Report Volume III (Portland MSS):  contains the official parliamentary despatch of the battle from the Committee of Safety in London to its counterpart in Herefordshire on 15 November 1642.

John Lilburn’s accounts: can be found in in Cobbett’s state trials and British Library Thomason Tracts E314/2.  Lilburn served in Lord Brooke’s parliamentary regiment at Brentford.

Other useful Thomason Tracts include parts of E74, E127 and E126.

LIST OF SOURCES

• Alnwick U.1.6/20 (Household accounts of Syon House 20th January 1642/3 to 20th January 1643/4)
• Ashmole MS 830 folio 292-293
• A True and Perfect Relation of the Barbarous and Cruell Passages of the Kings Army at Old Brainceford, 1642
• British Library, Thomason Tracts E242/11 A Perfect Diurnal of the Passages in Parliament, 1642
• British Library, Thomason Tracts E127/19 The Valiant Resolution of the Seamen Under the Command of the Earle of Warwick, 1642
• British Library Thomason Tracts E127/21 Certaine Speciall and Remarkable Passages … 12-18 November 1642
• British Library, Thomason Tracts E127/24 A declaration and manifestation of the proceedings of both armies, 1642
• British Library, Thomason Tracts E127/35, Speciall Passages and Certain Informations from Severall Places…Tuesday 15 November - Tuesday 22 November 1642
• British Library Thomason Tracts E314/2 Innocency and Truth Justified, 1645
• British Library Thomason Tracts E73(4) God In the Mount or a Continuation of England’s Parliamentary Chronicle
• Complete Collection of State Trials, Cobbett London 1809 Vol IV pg 1270-1470 The Trial of Lt Col John Lilburne 24-26 October 1649 at the Guildhall
• Cornwall Record Office DDT (Tremayne of Heligan) 1609/1
• Guildhall Library Pam 1137 Speciall Passages and Certain Information from Severall Places (Tues 8 November - Tuesday 15 November 1642), 1642
• Historical Collections Part 3 1642-1644 Vol II,  John Rushworth, 1659
• Historical Manuscripts Commission 29th Report Volume III (Portland MSS)
• Historical Manuscripts Commission:  Calendar of the Marquess of Ormonde Vol II New Series (1903)  A Brief Relation of the Life and memoirs of John Belasyse Written and Collected by His Secretary Joshua Moore
• Historical Notices (Vol II), Nehemiah Wallington, 1869
• History of the Great Rebellion - Edward Hyde, Earl of Clarendon (Oxford University Press), 1967
• Life of James II (Vol I) - Rev J S Clarke, 1816
• Memorials of the English Affair - Bulstrode Whitelock, 1682
• Memoirs of Edmund Ludlow - Edmund Ludlow, 1668
• Memoires of the Reign of King Charles I - Sir Philip Warwick, 1701
• Memoires of the Lives, Actions, Sufferings and Deaths of those noble, reverend and excellent personages that suffered by death, sequestration, decimation or otherwise for the protestant religion, and the great principle thereof, allegiance to their soveraigne, in our late intestine wars, ... and from thence continued to 1666. With the life and martyrdom of King Charles I,  David Lloyd. Canon of St. Asaph, 1668
• Military Memoirs of the Great Civil War: Being the memoirs of John Gwyn - John Gwyn (Ken Trotman) 1987
• Royalist Ordnance Papers, ed. Ian Roy, (Oxfordshire Record Society), 2 Vols, 1964, 1975
• Somer’s Tracts (Vol V), ed. Walter Scott, 1809
• The English Civil War: A Contemporary Account Vol 2 1640-1642 - Edward and Peter Razzell (Eds) (Caliban Books), 1996